Infra red imaging from police helicopters has reportedly shown that only one in 10 tents pitched outside St Paul's Cathedral as part of the 'Occupy London' protest are actually occupied over night.

A video shot by police helicopters was said to show around only 20 of the 200 tents on the encampment with people sleeping in them overnight, suggesting many protesters are returning to the warmth of their London homes.

City of London police have declined to make the images public. But the Daily Telegraph took things into its own hands and slipped into site with its own thermal imaging camera.

Footage shot by the paper at 12.30am Tuesday morning appears to show much of the camp deserted.

After being confronted by protesters, the Daily Telegraph's reporter was forced to retreat from the camp.

But the accusations have been rejected by the protesters on Twitter. The official OccupyLSX Twitter account tweeted: "Modern tents are designed to keep heat in. Those brave enough to withstand the cold in Tescos Value jobs may be detectable."

Robin Smith, a 48-year-old former Conservative councillor for Wokingham Town Council, told the Press Association he was one of many part-time protesters at the camp.

"I'd say about 25% of the people go away and come back. There are lots of normal middle-class people turning up and helping but they have to go back home and some people come once and go away," he said.

"They've got jobs and a family to keep, so they've got to look after their kids or go to work. I met one guy who comes in then goes home to go to work."

St Paul's has decided to close its doors to the public for health and safety reasons, a decision "unprecedented in modern times" according reverend Graeme Knowles.

But the protesters claim they have become a tourist attraction which is in fact helping businesses around the church boom.

Local MP Mark Field suggested police should perhaps seize on the allegation that the camp was mostly deserted at night and move in to clear it then, in order to minimise trouble.

Field said he had no problem with people protesting, but expressed concern it was turning into a "semi-permanent encampment" that was disrupting a "key iconic tourist site".

"Perhaps nighttime is the right time to get the camp cleared," he said.