Meeting the house-building targets imposed on the Bristol region by the Government would take 123 years under current construction rates.

Just 238 new houses were started during the last quarter, according to the National House Building Council, down by 61 per cent on the same period last year.

If such a low level continues, the unpopular central Government ruling that 117,000 must be built locally by 2026 would actually take until 2131 to be fulfilled.

Nationally, around 270,000 houses must be built every year if the original target of three million is to be achieved but only about 100,000 have been registered this year.

Grant Shapps, the Shadow Housing Minister, who uncovered the figures, said: "I think it's an absolutely terrible way to go about planning housebuilding, to set a national target here and then try to force those numbers down through the regions.

"It was never going to work anyway but the housing crash has made it even less likely."

Thousands of residents have signed petitions calling for the Government to ditch the regional spatial strategy that sets out how many homes must be built across the former Avon area.

Ministers argue it will provide much-needed homes and will help first-time buyers struggling to get on the housing ladder. But critics claim it will lead to prime green-belt sites being developed.

Debbie Nicholls, of Dundry Residents' Action Group (DRAG), said the housebuilding figures showed it was time for the Government to look again at the plans. She said: "These targets are unsustainable. We are not against new houses but we are against the green belt being built on to meet them."

The Conservatives warned the Government's whole approach to housing needed to be reviewed. Mr Shapps claims that the seeds of the next housing downturn were being sowed now because once skilled workers are lost the prices will be pushed up when demand begins to rise again.

He called for the Government to "think creatively" about how it could help to boost the industry through social housing developments.

Mr Shapps said: "If you allow the sector to collapse it is almost impossible to re-build it in time for another housing bubble because the skills will leave the industry.

"Afterwards, as demand picks up again, the skills won't be there to build the homes we need and house prices will start to go up much too quickly again.

"Government clearly has a role to play. The Government needs to be more proactive in coming forward with plans to kick-start the market and prevent this industry from melting down."

A Communities and Local Government spokeswoman said: "Despite the current economic conditions, if we do not build more homes in the long-term then the housing ladder will get even further out of reach, leaving the next generation with nowhere to live. The South West has a real housing issue – it is the only region with above average house prices and below average incomes.

"We need a long-term development vision that addresses housing shortages, tackles the threat of climate change and strengthens the region's economy. We are committed to ensuring that everyone has access to a decent home at a price they can afford, in a place where they want to live and work."