Brokers have expressed caution about the help-to-buy Isa, which is due to be launched in December.
Six banks have signed up to provide the Treasury’s scheme, but some brokers have expressed concern that they will use the opportunity to push their products onto savers.
David Hollingworth, associate director of Bath-based London & Country Mortgages, said: “What we don’t know is what the products look like and whether they will appeal to savers.
“Without a shadow of a doubt, help-to-buy Isa customers will be given incentives to take out a mortgage with their provider, but borrowers need to look around.
“A sweetener doesn’t guarantee that a mortgage will be the right deal.”
Jane King, a mortgage adviser with London-based Ash Ridge Private Finance, said the scheme – which will allow first-time buyers to save up to £200 a month which the government will top up by 25 per cent up to a maximum of £3,000 – will not make much difference to those looking for a home in London or the South East.
“More and more of my buyers are getting money from their parents or from inheritance, and this wouldn’t make much of a dent in the deposit,” she said.
“The banks are bound to push their mortgages onto savers and it is probably one of the reasons they are taking part.”
The five banks and one building society taking part in the scheme, which launches on 1 December, are Barclays, Lloyds Banking Group, Nationwide, NatWest, Santander and Virgin Money.
Chancellor George Osborne said: “This government is determined to help working people, and encouraging the aspiration to home ownership is central to that.”
The scheme was announced in this year’s March Budget.
Stephen Noakes, managing director for retail customer products at Lloyds Banking Group, said: “We know that raising a deposit is the key barrier when trying to buy a first home, and the help-to-buy Isa will reward positive savings behaviour and make a real difference in helping young people get onto the property ladder faster.
“We are fully committed to providing this valuable assistance to our customers.”
Only first-time buyers who are buying a home worth up to £250,000 – or £450,000 in London – will be eligible.
The scheme can be used in conjunction with other government schemes to help people get on the property ladder, including the other elements of help-to-buy and shared ownership schemes.