The scheme was designed to kick-start the housing market and help first time buyers. It has, however, also been partly blamed for the boom in house prices.
Property asking prices rose to a new record high in March, with average asking prices reaching £552,530 ($917,714) in London which is £8,298 above the capital's previous high, reached last October.
"The extended time frame of the scheme will aid the progression of larger and longer-term development schemes," said head of U.K. residential research at Knight Frank, Grainne Gilmore.
(Read more: Bovis ups dividend as UK housing market booms)
"The question now is whether the Chancellor will adjust the parameters or the £12.5 billion set aside for Help to Buy part 2, the mortgage guarantee, to cover the additional £6 billion cost of this four-year extension to the equity loan," she said.
Across England and Wales, asking prices are 6.8 percent or £16,251 higher than a year ago and in London they have seen annual growth of 11.3 percent, according property website Rightmove.
Rising house prices have fueled stratospheric gains for shares in U.K. homebuilders, with Barratt Developments up just over 80 percent in the last year. Persimmon and Taylor Wimpey have also seen their share price surge over 40 percent.
"There is a lot of positive stories coming out of the property market, there was a very long and pronounced period of underbuilding and there is a big boost to demand, so you can see a story to back up the movements," said head of portfolio strategy at Brewin Dolphin, Guy Foster.
—By CNBC's Jenny Cosgrave: Follow her on Twitter