LONDON (Reuters) - British house prices are likely to fall seven percent this year and will probably tumble 20 percent from their highs before they start to recover, a Reuters poll found, in more evidence that a decade-long boom has turned to bust.

The poll of 27 analysts at banks, investment firms and research institutions found forecasts for 2008 as a whole ranged from a 20 percent fall to a 2.2 percent rise, with a fall of eight percent predicted for next year.

The poll found economists predicting the market would fall 20 percent from peak to trough, with a few saying the correction would be as much as 35 percent.

A Reuters survey in May predicted just a five-percent fall in house prices this year, while a poll in October forecast a 2.2-percent rise, highlighting the rapidly deteriorating outlook for the once-booming British property market.

But the figures may already be understating reality. Data released by the Halifax mortgage lender earlier yesterday showed house prices fell for the sixth month in a row in July and by a sharp 1.7 percent.

Some are now concerned that Britain is heading for a bust similar to the one that is in full gear in the US, where prices are already falling more than 15 percent on one measure, the worst on record.