By Bob Howard
BBC Radio 4's Money Box
Teachers and nurses in some parts of England are among the groups who will be given a new way to buy their first home next month.
The new scheme aims to help priority first time buyers
Rebecca Dungworth is a so-called "key worker", one of the groups which the government is trying to help become home owners.
She has been teaching for two years in London but was horrified at the price of properties in the capital compared to her native Somerset.
"I was paying a lot of money out each month and I wanted to purchase a property but I found this was impossible with my salary and the amount of mortgage I could actually receive," she told BBC Radio 4's Money Box.
The government's new Open Market HomeBuy project aims to boost the buying power of people like Rebecca by a third.
Eligible people will be able to take out a mortgage for 75% of the price of a property.
The government will then give them 12.5% as an interest-free loan and the lender will provide the other 12.5%, although its loan is only interest-free for the first five years.
No deposit will be required.
Andy Caton from The Yorkshire Building Society - one of the four lenders involved - admitted it is a complex arrangement: "It is complicated because you've got bits of a conventional mortgage, you've got parts of the mortgage being provided by equity loans from the government and you've got parts of the mortgage being provided by equity loans from ourselves."
When you come to sell, you have to pay back the original loans to the lender and the government.
You also have to pay them each 12.5% of any increase in value in your property.
Plus, Open Market HomeBuy is not transferable, so every time you move, you would have to repay and then apply for a new mortgage.
Public sector unions say that in places like London even boosting a person's purchasing power by a third would leave them a long way short of being able to afford to buy such a large stake in a property.
In the end, Rebecca has opted to purchase a 25% stake in a home with the help of a local housing association.
Heather Wakefield from Unison told the programme there are better ways for the government to be spending tax payer's money.
"Most of our members could not afford 75% of the cost of a property of any kind in London," she said.
"There needs to be housing available which is either home ownership with a much greater subsidy or at affordable rents."
The government says the scheme will help council and housing association tenants, and people on the housing register as well as key workers.
In the first 18 months it has pledged £230m and by 2010 it aims to have helped 20,000 people.
Government-appointed HomeBuy Agents will assess who will get priority in different areas of the country.
Yvette Cooper, the minister with responsibility for the scheme, says help for these categories of buyers is urgently needed:
"In the long run what you've got to do is build more homes but I don't think it's fair in the meantime to simply watch whilst some people get left behind and can't get on the housing ladder at all,"
So far, Yorkshire Building Society, Nationwide, Halifax/Bank of Scotland and Advantage - part of Morgan Stanley - have signed up to provide Open Market HomeBuy loans. They become available from the 2 October.
BBC Radio 4's Money Box was broadcast on Saturday 23 September 2006, at 1204 BST and will be repeated on Sunday, 24 September at 2102 BST.