Two damning reports warn that the target of 3m new homes across the country by 2020 may no longer be viable in the economic crisis and may be too damaging to the environment.

A Labour-dominated Commons committee says the plan setting out the target for building in the region should be suspended until the environmental impact of that scale of development is assessed.

It warns the pressure to meet housebuilding targets – which have been sharply increased at the Government's demand – means councils will be forced to abandon vast swathes of greenfield land which developers will cherry pick over brownfield sites.

In a separate report the Campaign to Protect Rural England (CPRE) accuses the Government of overriding the views of offic-ials in the region and calls for an end to top-down housing targets.

Referring to the Yorkshire target, the charity says: "It is unclear how central Government came up with its own housing figure, or, more importantly, how it can believe that the proposed figure can be delivered in the current economic climate and within the environmental limits of the region without serious consequences for the quality of life of those living there."

Housebuilding has come to a virtual standstill in recent months with banks reining in their mortgage lending, making the chances of meeting the flagship 3m homes target increasingly unlikely, especially amid anger at the targets being imposed from Whitehall rather than decided locally.

New Housing Minister Margaret Beckett last week appeared to leave room for it to be re-viewed when she insisted it was not a target but an "ambition". The department had previously described it as a "challenging but very achievable target".

In an effort to meet the 3m figure, Ministers have ordered the English regions to increase the number of homes planned in their Regional Spatial Strategies (RSS). The draft plan for Yorkshire and the Humber included 15,160 homes per year, later rising to 19,120. But the final version decreed the region must build 22,260 homes per year – more than 400,000 over 18 years.

Today's report by the Commons Environmental Audit Committee calls on the Government to insist on even higher environmental building standards and not wait until 2016 for all new homes to be zero carbon.

Committee chairman Tim Yeo said the targets had been set in a time of economic optimism and easy credit and the assumptions on which they were based must be reviewed in the new climate.

"This is an opportunity for the Government to place environmental concerns at the heart both of targets and planning regulations for new housing."

Sticking with high nationally-imposed targets risks making it impossible for local authorities to refuse planning permission even on land "that is not currently needed and that would not otherwise be granted", his report said, adding that developers are likely to prefer to build on greenfield sites rather than within existing settlements.

The report also demands a renewed commitment to maintaining the existing green belt, warning that building on it and installing new green belt elsewhere is not good enough.

Yorkshire and Humber Housing Board chairman Coun Kris Hopkins said: "We're extremely concerned about the impact these huge arbitrary figures would have on our greenfields. There's no doubt there's a need to build more homes, but a top-down figure is not the way to do it."

The CPRE claims if the present targets for the region are maintained up to 7,791 homes a year will be built on greenfield land.

Fiona Howie, its senior regional policy officer, said: "We do need more homes, but they should be delivered in a way that will not damage the environment and people's quality of life."

The Department for Communities and Local Government in-sisted it was committed to green building. Building on brownfield land would remain the priority. It dismissed the CPRE analysis as "flawed and one-sided".

Mrs Beckett said: "Now is not the time to scale back on long-term ambitions because of current economic difficulties. We need to be ready for the recovery...

"Those who argue against more homes need to seriously think about the future consequences for families on waiting lists, or those living in overcrowded homes, or struggling to get on to the housing ladder."