The one thing to remember when walking along the back of an Antonov AN2 military aeroplane while it flies 8,000 feet above Moscow is that the wind up there plays havoc with your nasal passages. No amount of Vick's Sinex can prepare you for what will happen in the Russian clouds.

'Snot,' said Herbie Pitts. 'Big hazard. Nothing you can do about it, it ends up all over your face, hair, ears. I mean everywhere.'

Herbie Pitts knows this because he has spent the last two summers messing around on Antonovs as they fly about their business. Up to four times a day he has been air- borne, climbing out through the top of the plane's cockpit unencumbered by parachute or safety harness and then clambering back towards the tail. Once in position, on the foot-wide refuelling walkway which runs along the top of the aircraft, he would go through his balletic routine, strutting around like Freddie Mercury, performing acrobatics to music played through Walkman headphones taped to his ears. Then, once back on the ground, he would take a handkerchief to his face.

No one was paying him to do this, no one was watching him, this is his hobby, a hobby on which he has spent pounds 30,000 in the past two years. He is, he says, an 'aerial exhibitionist'.

'I used to call myself an 'artiste of the clouds' but that sounded a bit tarty,' he said. 'What I do lay claim to being is without doubt the first Westerner to stand on one leg on an aircraft over Moscow.'

And probably the last.

Getting up above Russia was the conclusion of a 12-year obsession for Herbie, 29.

'It's been my whole life,' he said. 'I have no friends, no social life, no possessions. I work every minute I can as a freelance gardener - pounds 4 an hour - to finance this thing. I have nothing in my life but plane-walking.'

Herbie's obsession began when he was a teenager and he became fascinated by the Barnstormers, a circus troupe which travelled America in the Twenties doing unlikely things with leftover First World War flying stock. While other boys of his age hero-worshipped Gary Lineker or Lemmy from Motorhead, Herbie took

as his role model Charles O'Timmons, a one-legged, one- armed wing-walker.

'He was the ultimate,' said Herbie in his flat Surrey vowels, oddly reminiscent of John Major. 'On one occasion his artificial leg went through the wing during a flight and got caught in the control cables. He couldn't free it, so he unbuttoned his trousers, unbuckled the leg and hopped back into the cockpit, trouserless. Cool or what.'

As both his parents worked at Heathrow, Herbie used to go along most weekends and watch the planes landing, dreaming of doing an O'Timmons on the back of a Jumbo. And he would attend meetings of his local Air Training Corps, spending hours crawling on an old plane which was rusting away in the car park, doing Barnstormer poses to the amusement of his mates.

Then, when he was 18, Herbie heard that one of Freddie Laker's redundant Boeing 707s was lying around in a Heathrow backlot. This was the spur he required: he hired it and spent the day messing around on its superstructure, mainly re-enacting sequences from Torvill and Dean's Bolero routine.

'Wing-walking is very like ice- dancing, it's all about balance, fluidity of movement,' he said. 'That afternoon, I knew I had the confidence to do it. I reckoned I could become a Barnstormer.'

This, despite the fact the plane remained grounded all day.

'True,' he said. 'But remember it was a 20ft drop down to the ground. Frankly, falling from 20 feet is not much better for you than falling from 8,000 feet.'

Charged with enthusiasm, Herbie then set out to find himself a 707 he could put in the air. Getting a plane wasn't a problem, Nigerian Airways agreed to charter him one for dollars 2,000 an hour. The money wasn't a problem, either, as he had constructed an elaborate network of credit cards to finance his plot ('I found if I kept applying to Barclaycard, they kept sending me one; I had 20 at one time'). The problem was red tape: regulations in Britain, he found, spoil- sportingly prevent teenagers cavorting around on the back of air- borne passenger airliners.

''I tried to find out where I could do it,' Herbie remembered. 'There was nothing, nowhere. So I tried to start an aerial exhibitionists' club, you know co-ordinate fellow enthusiasts, swapping information that sort of thing. It turned out there wasn't anyone else out there.' Strange, that.

Undeterred, Herbie got himself a job as an engineer at Heathrow, and fuelled his habit by spending his lunch-breaks strutting on grounded planes. In the evenings he began a worldwide telephone search for a territory where air-traffic restrictions were less stringent than in Britain. In Africa, he discovered, he could do it, but the costs were prohibitive; in Latvia the head of an airline offered him a plane in exchange for marrying his daughter so she could land British citizenship. But two years ago, he found his grail: Russia, where deregulation has reached the point of anarchy and foreign exchange enables you to do anything, even going to a military airfield outside Moscow, hiring an old plane, plus pilot, navigator and interpreter for the purpose of wing-walking.

Thus last summer, having packed in his job and sold up everything, Herbie went to Russia and made his first flight.

'The pilots in Russia are top,' he remembered. 'My first looked at me a little strangely and said he had never met anyone like me. But he did a brilliant job. When we got up to the cruising height, he gave me a nod and I climbed out and reached the point of no return. I kind of hovered there thinking that it was my last chance to turn back and that maybe standing on one leg in my bedroom wasn't the fullest preparations for standing on one leg 8,000 feet above Russia. But at the same time this was the culmination of 12 years' search. If I didn't do it, what was the point? So off I went.'

Weighed down by a huge Russian air force issue parachute, Herbie found he could hardly stand, let alone walk; his goggles weren't tight enough and blew down round his chin, meaning he was temporarily blinded by the wind; then the ski trousers he was wearing balloned out like wind socks and had to be released by his interpreter sticking her hands up through the cockpit roof. Not an auspicious start. Herbie loved every minute of it. 'It was fantastic, up out in the clouds, just wonderful.'

After half a dozen flights, Herbie decided to dispense with the parachute, and strap himself instead to a safety cable.

'But I got rid of that pretty soon,' he said. 'It was like mowing the lawn with an electric Flymo, the cable kept getting in the way. So now I go up there without any safety assistance at all, except the first-aid pack in the cockpit: some plasters, a tube of antiseptic and a packet of Nurofen. All you need really to plane-walk is confidence. Plus strong thighs, poor eyesight and no dependents.'

Next month, Herbie makes his last flight of the year (after September it gets impossibly cold). He has a trick in store, adding a prop to his usual routine, but he wants it kept quiet, because even in Russia, what he is planning to do is illegal. He hopes, however, to bring back photographic evidence of it.

'Mind you, I'll need better luck than the last load of pictures I had done,' he said. 'I wanted some close ups, so I hired another plane and a local photographer. To prevent getting the wing tips in the frame, the photographer was strapped out on the wing. He was terrified, but came down in one piece and handed over the film. I took it back to England, made sure it was OK through the X-ray machines and sent it to photographic laboratories for processing. A week later I got a new roll of film, but no prints. They had screwed up the developing. A letter said 'good luck with your hobby'. But I don't think they meant plane-walking.'

(Photographs omitted)