Call me childish, but I love all the nonsense - the snow, the trees, the tinsel, the turkey. I love presents. I love carols and cheesy songs. I just love Christmas™.

That's why I was so excited. And not just for me, but for Annie. Aylsa, her mum, said she didn't see the big deal and why was I a sentimentalist, but I knew Annie couldn't wait. She might have been 14, but when it came to this I was sure she was still a little girl, dreaming of stockings by the chimney. Whenever it's my turn to take Annie - me and Aylsa have alternated since the divorce - I do my best on the 25th.

I admit Aylsa made me feel bad. I was dreading Annie's disappointment. So I can hardly tell you how delighted I was when I found out that for the first time ever I was going to be able to make a proper celebration of it.

Don't get me wrong. I haven't got shares in YuleCo, and I can't afford a one-day end-user licence, so I couldn't have a legal party. I'd briefly considered buying from one of the budget competitors like XmasTym, or a spinoff from a non-specialist like Coca-Crissmas, but the idea of doing it on the cheap was just depressing. I wouldn't have been able to use much of the traditional stuff, and if you can't have all of it, why have any? (XmasTym had the rights to Egg Nog. But Egg Nog's disgusting.) Those other firms keep trying to create their own alternatives to proprietary classics like reindeer and snowmen, but they never take off. I'll never forget Annie's underwhelmed response to the JingleMas Holiday Gecko.

No, like most people, I was going to have a little MidWinter Event, just Annie and me. So long as I was careful to steer clear of licenced products we'd be fine.

Ivy decorations you can still get away with; holly's a no-no but I'd hoarded a load of cherry tomatoes, which I was planning to perch on cactuses. I wouldn't risk tinsel but had a couple of brightly-coloured belts I was going to drape over my aspidistra. You know the sort of thing. The inspectors aren't too bad: they'll sometimes turn a blind eye to a bauble or two (which is just as well, because the fines for unlicensed Christmas™ celebrations are astronomical).

So I'd been getting all that ready, but then the most extraordinary thing happened. I won the lottery!

I mean, I didn't win the lottery. But I was one of a bunch of runners-up, and it was a peach of a prize. An invitation to a special, licensed Christmas™ party in the centre of London, run by YuleCo itself.

When I read the letter I was shaking. This was YuleCo, so it would be the real deal. There'd be Santa™, and Rudolph™, and Mistletoe™, and Mince Pies™, and a Christmas Tree™ with presents underneath it.

That last was what I couldn't get over. It felt so forlorn, putting my newspaper-wrapped presents next to the aspidistra, but ever since YuleCo bought the rights to coloured paper and under-tree storage, the inspectors had clamped down on Aggravated Subarborial Giftery. I kept thinking about Annie being able to reach down and fish out her present from under needle-dropping branches.

Maybe I shouldn't have told Annie, just surprised her on the day itself, but I was too excited. And if I'm honest, partly I told her because I wanted to make Aylsa jealous. She'd always made such an issue of how she didn't miss Christmas™.

'Just think,' I said, 'we'll be able to sing carols legally - oh, sorry, you hate carols, don't you...' I was awful.

Annie was almost sick with excitement. She changed her online nick to tistheseason, and as far as I could work out she spent all her time boasting to her poor jealous friends. I'd peek at the screen when I brought her tea: the chatboxes were full of names like tinkerbell12 and handfulofflowers, and all I could see were exclamations like 'noooo!?!?!? crissmass?!?! soooo kewl!!!!!' before she blocked the screen demanding privacy.

'Have a heart,' I told her. 'Don't rub your friends' noses in it,' but she just laughed and told me they were arranging to meet on the day anyway, and that I didn't know what I was on about.

When she woke up on the 25th, there was a stocking™ waiting for Annie at the end of her bed, for the first time ever, and she came into breakfast carrying it and beaming. I took enormous pleasure in waving my YuleCo pass and saying, perfectly legally, 'Happy Christmas™, darling.' I was glad that the ™ was silent.

I'd sent her present to YuleCo, as instructed. It would be waiting under the tree. It was the latest console. More than I could afford but I knew she'd love it. She's great at video games.

We set out early. There were a reasonable number of people on the streets, all of them doing that thing we all do on the 25th, where you don't say anything illegal, but you raise your eyebrows and smile a holiday greeting.

Technically it was a regular weekday bus schedule, but of course half the drivers were off 'sick'.

'Let's not wait,' Annie said. 'We've got loads of time. Why don't we walk?'

'What have you got me?' I kept asking her. 'What's my present?' I made as if to peer into her bag but she wagged her finger.

'You'll see. I'm very pleased with your present, Dad. I think it's something that'll mean a lot to you.'

It shouldn't have taken us too long, but somehow we were slow, and we dawdled, and chatted, and I realised quite suddenly that we were going to be late. That was a shock. I started to hurry, but Annie got sulky and complained. I refrained from pointing out whose idea walking had been in the first place. We were running quite a while behind time as we got to central London.

'Come on,' Annie kept saying. 'Are we nearly there?'

There were a surprising number of people on Oxford Street. Quite a crowd, all wearing that happy secret expression. I couldn't help smiling too. Suddenly Annie was running on ahead, then coming back to haul me along. Now she wanted to speed up. I kept having to apologise as I bumped into people.

It was mostly kids in their twenties, in couples and little groups. They parted indulgently as Annie dragged me, ran on ahead, dragged me.

There really were an astonishing number of people.

I could hear music up ahead, and a couple of shouts. I tensed, but they didn't sound angry. 'Annie!' I called, nonetheless. 'Come here, love!' I saw her skipping through the crowd.

And it was really a crowd. Was that a whistle? Where'd everyone come from? I was jostled, tugged along as if all these people were a tide. I caught a glimpse of one young bloke, and with a start of alarm I saw he was wearing a big jumper with a red-nosed deer on it. I just knew to look at him he didn't have a licence. 'Annie, come here,' I was calling, but I got drowned out. A young woman next to me was raising her voice and singing a note, very loud.

'Weeeeee...'

The lad she was with joined in, and then his friend, and then a bunch of people beside them, and in a few seconds everyone was doing it, a mixture of good voices and terrible ones, combining into this godawful loud squeal.

'Weeeeee...' and then, with impeccable timing, all the hundreds of people sort of caught each others' eyes, and their song continued.

'...wish you a merry Christmas, We wish you a merry Christmas...'

'Are you mad?' I screamed, but no one could hear me over that bloody illegal rumpty-tum. Oh my god. I knew what was happening.

We were surrounded by radical Christmasarians.

I was spinning around, shouting for Annie, running after her, looking out for police. There was no way the streetcams wouldn't spot this. They'd send in the Yule Squad.

I saw Annie through the crowd - goddammit, more people kept coming! - and ran for her. She was beckoning to me, looking around anxiously, and I was batting people out of the way, but as I approached I saw her look up at someone beside her.

'Dad!' she shouted. I saw her eyes widen in recognition, and then - did I see a hand grab her and snatch her away?

'Annie!' I was screaming as I reached where she'd been. But she was gone.

I was panicking: she's an intelligent girl and it was broad daylight, but whose was that bloody hand? I called her phone.

'Dad,' she answered. The reception was appalling in this crowd. I was bellowing at her, asking where she was. She sounded tense, but not frightened. '... OK... I'll be... see... a friend... at the party.'

'What?' I was yelling. 'What?'

'At the party,' she said, and I lost the signal.

Right. The party. That's where she'd make her way. I controlled myself. I shoved through the crowd.

It was getting more bolshy. It was turning into a tinsel riot.

Oxford Street was jammed, I was in the middle of what was suddenly thousands of protesters. It took me anxious ages to make headway through the demonstration. What had seemed an anonymous mob suddenly sprang into variety and colour. Everyone was marching. I was passing different contingents.

Where the hell had all these banners come from? Slogans bobbed overhead like flotsam. FOR PEACE, SOCIALISM AND CHRISTMAS; HANDS OFF OUR HOLIDAY SEASON!; PRIVATISE THIS. One placard was everywhere. It was very simple and sparse: the letters TM in a red circle, with a line through them.

She'll be OK, I thought urgently. She said as much. I was looking around as I made my way toward the party, only a few streets away now. I was taking in the demo.

These people were crazy! It wasn't that I didn't think their hearts were in the right places, but this was no way to achieve things. All they were going to do was bring down trouble on everyone. The cops would get here any moment.

Still, I had to admire their creativity. With all the costumes and colours, it looked amazing. I have no idea how they'd smuggled this stuff through the streets, how they'd organised this. It must have been online, which means some pretty sophisticated encryption to fool the copware. Each different section of the march seemed to be chanting something different, or singing songs I hadn't heard for years. I was walking through a winter wonderland.

I went by a contingent of Christians all carrying crosses, singing carols. Right in front of them was a group of badly dressed people selling copies of a left wing newspaper and carrying placards with a photograph of Marx. They'd superimposed a Santa hat on him. 'I'm dreaming of a red Christmas,' they sang, badly.

We were beside Selfridges now, and a knot of people had stopped by the windows full of the usual mix of perfume and shoes. The demonstrators were looking at each other, and back at the glass. Over on a side street, a few passers-by were staring at the extraordinary spectacle. It brought me up short to see 'regular' shoppers - it felt as if there was no one but the marchers on the streets.

I knew what the Selfridges-watchers were thinking: they were remembering (or remembering being told - some of them looked too young to recall life before the Christmas™ Act) an old tradition.

'If they won't give us our Christmas windows,' one woman roared, 'we'll have to provide them ourselves.' And with that, they pulled out hammers. Oh god. They took out the glass.

'No!' I heard a man in a smart wool coat shouting at them. A contingent of the demo was looking horrified, laying down its banners, which read LABOUR FRIENDS OF CHRISTMAS. 'We all want the same thing here,' the man shouted, 'but we can't support violence!'

But no one was paying him any attention. I waited for people to steal the goods, but they just shoved them out of the way along with the broken glass. They were putting things into the windows. From bags and pockets they were taking little creches, papier-mâché Santas™, gaudily wrapped Presents™, Holly™ and Mistletoe™ and they were scattering them, making crude displays.

I moved on. A man stepped into my path. He was part of a group of sharp-dressed types at the edges of the crowd. He sneered and gave me a leaflet.

'INSTITUTE OF LIVING MARXIST IDEAS.

'Why We Are Not Marching.

'We view with disdain the pathetic attempts of the old Left to revive this Christian ceremony. The notion that the government has 'stolen' 'our' Christmas is just part of the prevailing Fear Culture that we reject. It is time for a re-evaluation beyond left and right, and for dynamic forces to reinvigorate society. Only last month, we at the ILMI organised a conference at the ICA on why strikes are boring and hunting is the new black...'

I really couldn't make head or tail of it. I threw it away.

There was the thudding of a chopper. Oh shit, I thought. They're here.

'Attention,' came the amplified voice from the sky. 'You are in breach of section 4 of the Christmas™ Code. Disperse immediately or you will be arrested.'

To my astonishment this was met with a raucous jeer. A chant started. At first I couldn't make out the words, but soon there was no mistaking them.

'Whose Christmas? Our Christmas! Whose Christmas? Our Christmas!'

It didn't scan very well.

I passed a group I recognised from the news, radical feminist Christmasarians dressed in white, wearing carrots on their noses: the sNOwMEN. A little guy ran past me, glancing around, muttering, 'Too tall, too tall.' He started to shout: 'Anyone 5 foot 2 or under come smash some shit up with the Santa's Little Helpers!' Another shorter man started furiously remonstrating with him. I heard the words 'joke' and 'patronising'.

People were eating Christmas™ pudding, slices of turkey. They were even forcing down brussels sprouts, just on principle. Someone gave me a mince pie. 'Blessed be,' yelled a radical pagan in my ear, and gave me a leaflet demanding that once we had won back the season we rename it Solsticemas. He was buffeted away by a group of muscular ballet dancers dressed as sugar-plum fairies and nutcrackers.

I was getting close to the venue where the party was supposed to be, but if anything there were even more people on the streets now. The place was going to be surrounded. How would we get in?

Figures were moving in on the crowd. Oh shit, I thought, the police. But it wasn't. It was an angry looking, aggressive bunch, smashing car windscreens as they came. They were dressed as Santa Claus™.

'Fuck,' muttered someone. 'It's the Red and White Bloc.'

It was obvious that the R&Ws were out for trouble. Everyone else in the crowd tried to draw away from them. 'Piss off!' I heard someone shouting, but they paid no attention.

Now I could see cops massing in the side streets. The Red and White Bloc were drawing them out, chucking bottles, screaming 'Come on then!' like pissed-up Football™ fans.

I was backing away. I turned, and there it was, the site for the party. Hamleys, the toy store. The armed guards who normally protected it must have run ages ago, faced with this chaos. I looked up and saw horrified faces at the windows.

I should be up there, I thought. With you. They were the partygoers. Kids and their parents, besieged by the demonstration, watching the police approach.

And oh, there was Annie, shouting to me, standing under Hamley's eaves. I wailed with relief and ran to her.

'What's going on?' she shouted. She looked terrified. The Yule Squads were approaching the provocateurs of the Red and White Bloc, banging their truncheons in time on tinsel-garlanded shields.

'Bloody hell,' I whispered. I put my arms protectively around her. 'There's going to be trouble,' I said. 'Get ready to run.'

But as we stood there, tensing, something astonishing happened. I blinked, and out of nowhere had come a young man in a long white robe. Before anyone could stop him he was between the ranks of the Red and White Bloc and the police.

'He's mad!' someone shouted, but all the hundreds and hundreds of people were beginning to hush.

The man was singing.

The police bore down on him, the R&Ws made as if to shove him away, but his voice soared, and both sides hesitated. I had never seen anyone so beautiful.

He sang a single note, of unearthly purity. He made it last, for long seconds, and then continued.

'Oh little town of Bethlehem, how still we see thee lie.'

He paused, until we were straining.

'Above thy deep and dreamless sleep, the silent stars go by.'

The R&W Bloc were still. Everyone was still.

'Yet in thy dark streets shineth the everlasting light...'

And now the police were stopping. They were putting their truncheons down. One by one they set aside their shields.

'The hopes and fears of all the years are met in thee tonight.'

More white-clad figures were appearing. They walked calmly to join their friend. With a start, I realised I was shielding my eyes. There was an implacable authority to these astonishing figures who had come from nowhere, these tall, stunning, uncanny young men. The white of their robes seemed impossibly bright. I could not breathe.

Now all of them were singing. 'How silently, how silently, the wondrous gift is giv'n. So God imparts to human hearts the blessings of His Heav'n.'

One by one, the police removed their helmets and listened. I could hear the frantic squawking of their superiors from the earpieces they removed.

'No ear may hear His coming, but in this world of sin...' The singers paused, until I ached to have the melody conclude. 'Where meek souls will receive Him still, the dear Christ enters in.'

The police were smiling and tearful amid a litter of body armour and nightsticks. The first singer raised his hand. He looked down at all the discarded weaponry. He declaimed to the Red and White Bloc.

'You should not have tried to fight,' he said, and they looked ashamed. He waited.

'You would have been trounced. Whereas now,' he continued, 'these idiots have disarmed. Now's the time to fight...' And he swivelled, and en masse, he and his fellow singers launched themselves at the police, their robes flapping.

The helpless cops gaped, turned, ran, and the crowd roared, and began to follow them.

'We are the Gay Men's Radical Singing Caucus!' the lead singer yelled in his exquisite tenor. 'Proud to be fighting for a People's Christmas!'

He and his comrades began to chant: 'We're here! We're choir! Get used to it!'

'It's a Christmas miracle!' said Annie. I just hugged her until she muttered 'Alright Dad, easy.'

Behind me the crowd were shouting, taking over the streets.

'That's the trouble with the Red and White Bloc,' muttered Annie. 'Bloody "strategy of tension" my arse. Bunch of anarchist adventurists.'

'Yeah,' said a boy next to her. 'Anyway, half of them are police agents. It's the first principle, isn't it? Whoever's arguing fiercest for violence is the cop.'

I was gaping, my head swinging between the two of them as if I was a moron watching tennis.

'What...?' I said finally.

'Come on Dad,' said Annie. She kissed me on the cheek. 'You'd never have let me go otherwise. I had to get you to walk here or we'd have been too early. Trapped like them.' She pointed at the still-staring prize-winners in Hamley's top floors. 'And then I had to run off or you'd never have let me join in. Come on.' She took my hand. 'Now that we bust through the police lines, we can reroute the march past Downing Street.'

'Well then, it's the perfect opportunity to get out of here...'

'Dad,' she said. She looked at me sternly. 'I couldn't believe it when you won that prize. I never thought I'd have a chance to be down this way today.'

'Someone grabbed you,' I said.

'That was Marwan.' She indicated the young man who had spoken. 'Dad, this is Marwan. Marwan, this is my dad.'

Marwan smiled and shook my hand politely, shifting his placard. MUSLIMS FOR CHRISTMAS, it said. He saw me reading it.

'It's not that much of a big deal for me,' he said, 'but we all remember how this lot came out for us when Umma plc tried to privatise Eid. That meant a lot, you know. Anyway...' he looked away shyly. 'I know it's important to Annie.' She gazed at him. Ah, I thought.

'Marwan's handfulofflowers, Dad,' she was saying to me. 'Off the internet.'

'Look, I have to tell you I'm pretty annoyed about all this,' I said. We were getting close to Downing Street now. Marwan had said goodbye at Trafalgar Square, so it was just the two of us again, along with 10,000 others. 'I bought you, I, I've lost a lot of, there's a big present in that party...'

'To be honest with you, Dad, I don't really need a new console.'

'How did you know...?' I said, but she was continuing.

'The one I've got is fine. I mostly use it for strategy games anyway, and they're not so power-hungry. Besides, I've got all the pinkopatches in my machine. It would be a pain in the arse to transfer them, and downloading them again is too risky.'

'What patches?'

'Stuff like Red3.6. It converts a bunch of games. Turns SimuCityState into RedOctober. Stuff like that. I'm already up to level 4. The end of level baddy's a Tsar. As soon as I can work out how to get past him I'll have got to Dual Power.'

I gave up even trying to follow.

At the entrance to the prime minister's residence was a huge Christmas Tree™, in white and silver. Everyone began to jeer as we approached. The army were guarding it, so people made sure the booing was good humoured. Someone threw Christmas pudding, but everyone sorted him out sharpish.

'That's not what Christmas looks like!' we all shouted as we went past. 'This is what Christmas looks like!'

As the skies darkened, the crowd was beginning to thin a bit, before the police could regroup. We went through a contingent all in red bandanas, and joined in with their singing. 'Deck the halls with boughs of holly, tra la la la laaa, la la la la. Tis the Season for the Internationale, tra la la la laaaa...'

'Still,' I said, 'I'm a bit sorry you didn't get to see the party.'

'Dad,' said Annie, and shook me. 'This was the best Christmas ever. Ever. OK? And it was so lovely to have it with you.'

She looked at me sideways.

'Have you guessed yet?' she said. 'What your present is?'

She was staring at me, very seriously, very intensely. It made me quite emotional.

I thought of everything that had happened that day, and of my reactions. Everything I'd been through and seen-been a part of. I realised how different I felt now than I had that morning. It was an astonishing revelation.

'Yes...' I said, hesitantly. 'Yes, I think I have. Thank you, my love.'

'What?' she said. 'You've guessed? Shit.'

She was holding out a little wrapped package. It was a tie.

Award winning author China Miéville's new novel, Iron Council, has just been published by Macmillan.