The stamp duty holiday on properties costing up to £175,000 was today extended until the end of this year.

The stamp duty holiday on properties costing up to £175,000 was today extended until the end of this year.

Chancellor Alistair Darling said the exemption meant that 60% of homebuyers would not be liable for the tax.

The threshold at which the tax kicks in was initially increased from £125,000 to £175,000 for one year in September 2008.

The extension was part of a series of measures to help boost the housing market and beleaguered construction sector.

Mr Darling also announced £500 million of extra financial support to kick-start building on housing projects which have stalled because of the credit crunch, including £100 million for councils to build new energy-efficient housing.

Many private developments have either been mothballed or not started at all as builders struggle under the problems in the financial markets, which have made it harder for people to raise the mortgage finance they need to buy a new home.

Building companies have seen their share prices plummet amid concerns that they could breach their banking covenants, while they have also been forced to write down the value of their land banks and the sector has shed thousands of jobs.

The problems in the housebuilding sector have put pressure on Government targets to have 240,000 new homes a year built by 2016, with just 105,000 new homes started in England during 2008.

The Government also announced that it was allocating an additional £80 million to HomeBuy Direct, its shared equity mortgage scheme, which aims to help first-time buyers get on to the property ladder.

Other measures to help homeowners included increased support for mortgage interest payments for people who have lost their jobs and are looking for work.

Moves to help the housebuilding industry, which the Government claims will lead to an additional 10,000 homes being built in England in the coming two years, were welcomed.

Stewart Baseley, executive chairman of the House Builders Federation, said: "We are delighted that money has been made available to unlock mothball sites.

"We now need to work with Government to identify sites and get work started as quickly as possible. The benefits of doing so are quite clear in terms of employment and for the wider economy."

The National Housing Federation said the Government had taken a step in the right direction but had not been bold enough.

Federation chief executive David Orr said: "The Government is right to take a stake in housing projects where work has stalled and to make it easier for social housing to be built, but ministers needed to go further.

"We are in the midst of major economic and housing crises and the Chancellor should simply have backed our call to spend £6.35 billion of public money on helping housing associations deliver 100,000 new social homes over the next two years.

"We now fear that because the Government has failed to back a comprehensive house-building programme the number of homes delivered this financial year will slump to an 88-year-low of 70,000, while the number of people on social housing waiting lists will simply soar to unparalleled levels."

Mr Darling was also criticised for extending the stamp duty holiday on homes costing up to £175,000, rather than reforming the tax altogether.

Adrian Coles, director-general of the Building Societies Association, said the extension of the exemption would not boost the housing market "substantially".

He said: "The BSA urges the Government to take this a step further by researching how the stamp duty system could be reformed to reduce the distortions from the current 'slab' structure of the tax that results in the bunching of transactions at prices just below the thresholds for different rates."

Peter Bolton King, chief executive of the National Association of Estate Agents, said: "Merely extending the stamp duty threshold is disappointing.

"In this difficult economic time, Mr Darling could have seized the opportunity to encourage first-time buyers to the market and to send a signal of confidence that may have reverberated around the economy."

Gillian Charlesworth, director of external affairs at the Royal Institution of Chartered Surveyors, said: "Extending the stamp duty holiday may help some buyers who do now seem to be entering the market but will only have a major impact if steps to increase levels of mortgage lending are also effective."

The Council of Mortgage Lenders described the Chancellor's measures to help the housing market as "modest", and added that while they were helpful, they were unlikely to have much impact overall.