On the approach to each slip road they’d become accustomed to the familiar pattern of a build-up of abandoned vehicles, trailing back down the exit run and out onto the motorway clogging all three lanes. Each time their progress was entirely blocked they were forced to unload the trailer and lift it over the central barrier between them and proceed along the oncoming lanes until they too, became impassable, then it was back over to the other side again. It seemed like every vehicle in London had ended up becoming ensnared on this motorway, caught bumper to bumper at every exit point.

Finally they came off at a junction that would take them into the city and, eventually, down to the Thames. There had been a frustrating half an hour trying to ease the trailer through a logjam of vehicles and around a barricade; once more having to unload the trailer, lift it over and repack it. But since then the ride had been almost effortless; the gentle coasting whirr of their bicycle wheels along the empty road, the occasional clatter of chains shifting gear and catching, the crackle of glass granules beneath their tyres and the rustle of dried leaves wind-borne and stirring.

And every now and then, when she decided it was her turn with the iPod, she would get utterly lost in the soundtrack of her younger, happier days.

She grinned as she cycled; felt almost good - the music made the past feel tangible. For some reason it made some sort of a future feel almost possible. She began to ask herself what she was going to do if they really did see lights; whether she’d still want to part with the boys and head home.

Sunlight shone into her eyes, finding gaps through the thin veil of clouds; not too hot as they pedalled, but still T-shirt-warm when they occasionally stopped to catch their breath.

By early afternoon they took the next exit which, like all the others, was plugged with abandoned vehicles, on to another A-road heading west, roughly parallel to the Thames ten miles further south of them, into central London.

They soon discovered, though, that progress from this point on wasn’t going to be quite so easy. Although the road wasn’t so blocked that they needed to dismount and negotiate their trailer over or around any obstacles, there were enough cars and trucks left on the hard shoulder or skewed across one lane or another that it was a relentless weaving slalom for them.

By four in the afternoon, they were passing through a lifeless outer London, still and silent; terraced houses and three-storey blocks of flats lined both sides of the road, every last window smashed leaving dark eye-sockets out of which tattered net curtains fluttered.

Leona noticed how quiet the boys had become, particularly Jacob. The spirited chattering about computer games and comics had dropped down a notch as they’d left the motorway. Now they pedalled in sombre silence, listening to the soft whisper of a breeze whistle tunelessly through empty office windows. They exchanged wary glances every now and then when they heard the clatter of loose things caught by eddies inside.

They crossed a bridge over a wide estuary, watching the afternoon sun emerge to sprinkle dazzling shards of light across the still water. Tugs and barges lay askew on mud flats either side, gulls and terns stepping delicately between them across the silt looking for an evening meal. Over the bridge, the road dipped south bringing them ever closer to the Thames which they would have been able to see by now if it wasn’t for the buildings on their left: shopfronts with floors of office space perched on top and riverside warehousing.

As they rattled and weaved along the road, the office blocks either side of them grew taller and more claustrophobic, pressing in on the road and towering over a seemingly endless parade of gutted news-agents, pubs, pawnbrokers and bookmakers. The sun was hidden by the tall buildings, every now and then a winking amber eye staring at them through first-floor windows, across the offices of abandoned call-centre desks and cubicle partitions.

‘Hang on,’ said Leona quietly. She stopped and pulled out her road map once more, orienting it to match the direction they faced.

Nathan looked around, frowning as he did so. ‘Hey, I think I know this. This is, like, right near that big exhibition place.’

Leona nodded, her eyes on the map. ‘The ExCel Centre?’

‘That’s the one.’

‘What’s the eck-sell?’ asked Jacob.

She looked up at the junction they’d stopped at. Like every other, it was littered with all manner of pilfered junk, dragged out, examined and dumped some time during the last decade; tall weeds poking opportunistically up through gutter grilles, cracks and bulges in the crumbling tarmac road. Amongst the debris, the occasional small bundles of stained and sun-faded clothes, from which dark leathery twigs and tufted scarecrow heads protruded.

She spotted a rust-peppered street sign above a KFC. ‘Prince Regent Lane.’ She checked her map again. ‘The exhibition centre is just down at the end of this road.’

Jacob squinted. ‘Maybe that’s where the lights were coming from?’

Nathan nodded. ‘Could be. It’s a big-huge place, Jay, right on the Thames.’

‘They did those big exhibition things there,’ added Leona. ‘Ideal Home exhibition, a boating thing . . . it’s enormous. It might have been used for one of the safe zones.’

The three of them stared down the street.

Jacob looking from one to the other. ‘So, we should go and see, right?’

Leona debated whether, with the daylight they had left, they should settle themselves in for the night. They hadn’t seen a single soul since entering London, yet she felt the urge to find somewhere secure, somewhere they could barricade themselves in. Even if there were no people around she’d seen plenty of dogs of all shapes and sizes scattering nervously away at the sound of their approach and watching them warily from dark doorways as they passed. She certainly didn’t fancy camping out in the middle of the street tonight.

Looking at the others, neither did they.

On the other hand, she felt a burning urge to go take a look-see. According to the map the exhibition centre wasn’t far away, perhaps another ten or fifteen minutes down the road. And then they’d be there, right on the bank of the Thames, with a clear line of sight up and down the river for miles. If it wasn’t the ExCel building Mr Latoc had seen glowing at night, it could possibly be the O2 Arena, or perhaps one or other of the towers of Canary Wharf? Whichever building it was, if somebody was generating light enough to reflect off an overcast night sky, surely, from there, right on that famous bend in the Thames, they’d have the best chance of seeing it.

It was quite possible that they could be sleeping beneath powered lights tonight.

‘All right,’ she said. ‘We’ve got time to go check out the ExCel. It’s not that far from here.’

They climbed back on their bicycles and turned left into Prince Regent Lane. It reminded her of the main road near their home in Shepherd’s Bush; a party-mix of shops either side: halal butchers, Caribbean takeaways, a shop selling saris, another selling hijabs, a snooker club, a small open-air market with rows of empty wooden stalls, a video store, a supermarket, mosques and several off-licences elbowing each other for space.

Moments later, halfway down Prince Regent Lane, they caught sight of the top of the giant exhibition building above a squat row of two-storey shops; they could see sprigs of white support poles protruding above a long pale roof. Beside it they could see the tops of several quayside cranes that had, once upon a time, serviced the busy barges pulling into Victoria Docks.

It was still light, the combed-out cloudy veil now lit from below by a setting sun; a beautiful vanilla skyline of ripples and veins staining the world with a rich sepia warmth. Although Leona had secretly doubted they were going to find anything at all in London, doubted the city was busy rebuilding itself on the quiet, she found herself desperately hoping the waning light of day would trigger an automatic lights-on response from somewhere nearby. She almost began to believe that the pale roof of the exhibition centre was going to flicker to life at any second, bathed in the clinical glare of a dozen roof-mounted floodlights.

Their pace quickened.

Towards the end of the road the squat buildings gave way to flat open ground, a scruffy little playground full of waist-high grass and brambles growing up the rusting A-frame of a child’s swing. Beyond it was a railway track with a pedestrian bridge over the top that would lead them down rickety steps onto a large riverside parking area at the rear of the giant, warehouse-like ExCel Centre.

‘Oh, fuck!’ gasped Jacob. ‘It’s huge! I never seen a building this big!’

Leona remembered coming here once before, as a girl; she must have been ten or eleven, Jacob hadn’t even been born then. Mum and Dad had taken her along to some sort of horse and pony expo - to see whether she really did want to ‘get into horses’ or whether it was just another of her many passing fads.

‘We should leave the bikes and the trailer here,’ she said, ‘if we’re going over the bridge to get a closer look.’

‘I’ll get the gun,’ said Jacob. ‘Just to be safe.’

He retrieved it from the back of the trailer.

‘Give it to Nathan,’ Leona said. Jacob sighed before he handed it over.

‘Here.’

Nathan cocked it and slung the strap over his shoulder.

‘Okay?’ she said.

The others nodded silently, quickly kicking their bike stands down. As their feet rang noisily up the metal steps of the overpass she looked along the railway line below, sleepers lost beneath a carpet of tangled green, and at the small Docklands Light Railway station several hundred yards away. She recalled stepping out onto the platform down there, excited by the sight of the giant white building towering over her and the convergence of so many other mums and daughters looking forward to their day inside.

So quiet now, though. No bustle and hubbub of expectant young voices, just the soft rumpling of a gentle breeze and the distant tap-tap-tapping of cables against the white flagpoles above the ExCel roof. They crossed over the train track and down the steps on the far side and into the parking area - another deserted expanse of failing concrete divided by flaking lines of yellow paint.

Leona nodded at the looming, featureless rear wall of the centre. ‘This must be the service entrance.’

Across the car-park their eyes drifted towards a quay with a safety rail running along it and beyond that the water of Victoria Docks, subdued and calm. Dazzling golden shards rippling across the still surface reflected the bedding sun, fat, orange and undulating like the hot wax of a lava lamp, looking to settle for the night.

Jacob nodded towards the quayside rail. ‘Race you, Nate.’

The boys cut across the car-park, finally clattering against the railing on the far side, whooping with delight, claims of victory and counterclaims bouncing back at them from the rear of the ExCel Centre.

She joined them a moment later, gazing out across at the docks. On the far side, a row of antiquated cranes stood tall and aloof; an industrial-age silhouette of spars and counterweights, swaying rigging chains and the vaulted roofs of dock warehouses that cast a long deep shadow across the water towards them.

From where they stood, panting and resting against the railings, they had an uninterrupted view of the skyline of the city, looking east along the curving Thames and west towards the mirror-smooth towers of Canary Wharf, glistening crimson from the glare of the setting sun.

Leona cupped her eyes as she took it all in, suddenly aware she was holding her breath in anticipation as she intently scanned the urban horizon for any signs of life.

London looked beautiful. She realised her heart ached for this place to come alive once more. For quayside street lamps to glisten proudly along the waterfront, for expensive dockside flats to once more cast smug balcony spotlights down onto even more expensive yachts. But instead, the three of them were staring at a darkening, lifeless, horizon.

Not a single light amongst the gathering gloom. Not even a torch beam or a candle or a campfire.

Jacob turned to his right to look at the exhibition centre. ‘Looks just as dead as everywhere else,’ he said, his voice carrying the weight of disappointment they all felt.

‘Perhaps the man lied to you two,’ she replied. ‘Told you what you wanted to hear.’

‘Great,’ grunted Nathan flatly.

The boys continued their vigil in silence. Still looking, still hoping. The reflection of the almost-gone sun glinted off a far away window, teasing them for a moment.

‘I’m sorry,’ she added softly. ‘If the city centre was recovering I’m sure we’d have seen something from here.’

Jacob’s lips clamped angrily. ‘Shit!’ He suddenly screamed, banging the rail with his hands. ‘Shitshitshit!!’ His voice echoed across the car-park.

She put an arm around his lean shoulders; they were shaking, trembling with rage.

‘Why?’ His voice broke as tears rolled down his cheeks. No longer the fresh baritone voice of a young man, but the heartbroken cry of a boy. ‘Why not by now, Lee? Why not? It’s been ten years!’

She shook her head. ‘I don’t know, Jake. Maybe there just isn’t anyone left in London now.’

They’d not spotted a single telltale sign of life all day; no rooftop vegetable gardens, no parks turned into allotments that Leona had half expected to find, no smudges of smoke in the sky, no give-away odour of woodsmoke or burning rubber - the kind of smell that can travel for miles and miles.

Nothing.

‘Maybe we could go and take a look inside the ExCel,’ she said, squeezing his shoulder gently. ‘There may be some things we can forage for. Then, we should find someplace for tonight.’

‘What about tomorrow?’ asked Nathan. ‘What we goin’ to do?’

Jacob angrily wiped his cheeks dry and steadied himself with a deep breath. He turned to Nathan and they exchanged a wordless acknowledgment of defeat, their faces both lifeless and spent; the naive energy that had driven them to race each other across the car-park felt stupid now.

‘We head back home, I suppose,’ said Jacob.

Leona nodded and smiled sadly. ‘Yes, home.’