It is a mystery to many how ordinary people can afford to live in the UK's capital. Consistently ranked one of the most expensive cities in the world, London's house prices are ever more ludicrous, even in these dark days of pay freezes, mass redundancies and bankruptcy.

Visit one of the campsites encircling the city and it becomes clear how some people make the sums work: by shunning bricks and mortar to live in tents, caravans and mobile homes.

Each morning at these sites the shower blocks teem with commuters washing, shaving and making themselves presentable for a hard day's graft in the big smoke.

Last week a council worker called Philip Hanman hit the papers when he claimed he had been forced out of his job after his bosses discovered he was commuting to work in Barking and Dagenham in east London from a campsite in Epping Forest, where he slept in a £30 tent. Hanman has taken voluntary redundancy from the council and now lives with his family in Cornwall, where he previously spent his weekends.

Camping commuters are far from rare in the capital. On the Lee Valley site in Edmonton, north London, near a monster branch of Ikea and surrounded by pylons, 40 pitches are reserved for "long-termers".

Many of them work constructing the Olympic park, driving buses or in other jobs in the city, returning to their "real" homes at the weekend.

Here, in a neat caravan, lives one of the more unusual residents. Last year Lucy Boggis, 21, spent her days chasing amateur athletes up a climbing wall in her role as Tempest in the Sky series of Gladiators. Now, she is devoting all her energy to the 2012 Olympics, where she hopes to represent Britain in the heptathlon.

With no lottery funding, money is tight. So last September she decided to set up camp at the Lee Valley site, which is next door to an athletics centre.

Each morning, she makes herself porridge on the small van's stove, before padding over to the shower block for a wash.

She's at the track for 9am, and spends the day practising the hurdles, high jump and the other five disciplines that make up her event. On the weekends she goes home to her family in the West Country. "Some of my fellow athletes take the mickey, but most of them actually think it's a good idea. If you don't have funding, you don't have much spare money, and it's much cheaper to stay in a caravan than rent a one-bedroom flat," she said.

Lee Valley is one of the more expensive sites around London, charging between £12.30 and £16.40 a night for a one-person pitch, depending on the season, plus £3.60 per day for electricity.

In a caravan a few doors down from Boggis lives IT contractor Keith Davidson, who commutes to Canary Wharf each day.

The City is less than an hour away by public transport, with a regular bus service stopping at the site and taking campers to the nearest station.

"My family lives up in Aberdeen, but I often get contracts down here. The main reason I stay here is because of the flexibility – if you rent a flat you often have to commit to six months or a year, whereas here you can come and go as you like," he said.

The campsite's only residency rules are that everyone has to clear off during the few winter months when the site is closed, and that you pay for every night you're taking up a pitch, whether you're there or not. In a motorhome nearby lives Bob Casbeard, who commutes a few days a week to his urban planning job in Hackney. "I've been coming here on and off for eight years," he said, showing off his retractable satellite dish and extensive cooking facilities. Unlike many of the other long-termers, Casbeard is not camping to save money – he owns houses in east London, Suffolk and the Champagne region of France. "I do it to save the planet," he said, pointing up to the solar panels on the roof.

He added: "It does save me some money, though. Sometimes I stay in a hotel in Chigwell, and it costs £70 a night, which even for three nights is more expensive than parking my van here for a whole week."