As the Chancellor Alistair Darling dithers over whether to gift borrowers a stamp duty holiday, housebuilders are falling over themselves to offer “freebies” to homeowners and buy-to-let investors in a desperate attempt to boost sales.

From promises to pay your mortgage for a limited period to offers of cash, the increasingly drastic measures reflect the panic of credit-crunched housebuilders as sales of new homes fall off a cliff. Buyers have dried up as mortgage rates have soared and house prices tumbled by more than 11 per cent since the peak of August last year.

And it looks as though there is worse to come, thanks in part to Mr Darling's indecision about stamp duty. Rumours that the Chancellor will suspend the tax in his Pre-Budget Report in the autumn have caused buyers to renege on transactions in the hope that there will be less duty to pay in the future.

Peter Bolton King, chief executive of the National Association of Estate Agents, says: “People who have already agreed to purchase a property are now asking what they should do. Consumers are confused and with this uncertainty transactions in the market will continue to slow down.”

Faced with this buying freeze some housebuilders will allow you to buy a home at a fraction of the purchase price. Others are offering to pay your mortgage for a number of years. Desperate developers will also contribute to deposits, cover your stamp duty and even offer a house exchange if you cannot sell your home in time. Some will even throw in a free car.

Shared-equity schemes are being offered by a number of housebuilders, such as Barratt Homes, Taylor Wimpey and Miller Homes. These allow you to buy a new home without having to pay the full purchase price upfront. You find the property you want and pay a set percentage of the price, typically 75 per cent. The balance is funded by a loan from the developer, which in many cases is interest-free for several years.

For example, if you were buying a £200,000 home from a developer offering a 75 per cent scheme, you could take out a standard mortgage for £150,000, with the other £50,000 lent to you by the housebuilder, say for ten years. The housebuilder's loan has to be paid back only if you decide to move house during the ten-year period. If prices have fallen when you want to sell, it will demand repayment of only 25 per cent of the value at that time, rather than the original value of the loan. But take care. If prices have risen by the time you sell, you will end up handing over part of your profits.

The potential problems do not stop there. At the end of the ten-year period you may be required to pay back the developer's loan. If you don't have the money, you will either have to sell your home or borrow the money elsewhere, storing up trouble for the future. Developers say that they will consider cases of financial hardship but they can repossess the property if the loan cannot be paid.

Some homebuilders allow the loan to continue but start charging interest. Taylor Wimpey, for example, charges 2 per cent over the Bank of England base rate after the ten-year period.

David Hollingworth, of London & Country, the mortgage broker, says: “There is a real danger that people will think that they can afford to buy without considering the need to pay off the loan.”

The best plan is to set up a savings plan to cover the loan, though the monthly cost could be a shock. To pay off £50,000 at the end of ten years would require monthly savings of about £300, assuming a 5 per cent return. That is on top of any mortgage payments.

Many of the incentives are aimed at first-time buyers. In recent months stricter lending rules have made it almost impossible to obtain a home loan without a deposit worth at least 10 per cent of a property's value.

Persimmon, the housebuilder, has teamed up with Halifax, the mortgage lender, to introduce a double-your-deposit scheme. Under the terms of the deal, Persimmon will stump up an amount equal to however much a first-time buyer saves in a Halifax instant-access account, to a maximum of £5,000. This will give buyers the chance to put as much as £10,000 towards their first deposit, provided that they use it to buy a Persimmon home.

However, experts say that the deal is of limited help to first-time buyers. On a £100,000 property, a £10,000 deposit would qualify buyers for a mortgage with most lenders. But on a property worth £200,000, the £10,000 would be only 5 per cent of the value, which would restrict the borrower to a handful of lenders. Ray Boulger, of John Charcol, another broker, says: “Unless borrowers have a 10 per cent deposit, they won't get a very good rate. This offer is likely to help towards the deposit, but it is unlikely to be enough without additional help from parents.”

Developers are also desperate to attract more investment buyers but are finding it difficult as landlords struggle to cover their monthly costs. Once again, interesting incentives are being thought up, but they come with a catch. Imagine Homes is offering to pay landlords' mortgages for the first five years if they buy one of its new-build properties. It promises to make 60 monthly payments to your account at a level equivalent to the cost of a five-year fixed-rate loan at 6.25 per cent.

Until recently it was difficult to obtain a mortgage at a rate of less than 6.25 per cent, so purchasers would still have had some costs to bear. But as rates have started to fall, this deal has begun to look like more of a winner.

Melanie Bien, of Savills Private Finance, another broker, says: “Imagine Homes assumes an 80 per cent loan-to-value ratio, but you can get a rate of 6.09 per cent for five years from Yorkshire Building Society with a loan-to-value ratio of up to 90 per cent. If you are buying a £200,000 property, you would have to put down a deposit of £20,000 and each month you would receive £833 from Imagine, whereas the actual cost of the mortgage would be £812, so you would be £21 ahead each month.”

However, this offer is limited to certain properties. Before you take the bait you need to be sure that these are suitable rental prospects that will earn enough in rent to cover your mortgage when the five years are up. The same goes if you are attracted by any other landlord incentives, such as guaranteed rents.

Ms Bien says: “If the developer is targeting landlords, you need to ensure that there is not going to be a glut of rental properties in your building after the incentives end. Ask yourself whether you will be able to rent out the property for a reasonable return that covers your outgoings. If the numbers don't add up, steer clear.”

Even with the incentives, you could struggle to find a decent mortgage. Most are available only on new-build properties. In recent years banks have become cautious about new-builds because of an oversupply of poor-value properties. Many lenders now require larger deposits on new-builds. Abbey, for example, has said that it will now lend up to only 70 per cent of a property's value - down from 75 per cent on new-build flats and 85 per cent on houses.

Mr Hollingworth says: “The advice to anyone tempted by these incentives is to remember that developers aren't really being generous, they are just desperately keen to get rid of unsold properties. A big incentive does not necessarily provide good value for money.”

What's on offer

Taylor Wimpey: shared equity scheme, half mortgage paid for two years and 6 per cent guaranteed rental yield until 2012.

Barratt: shared equity scheme, home-exchange package and will pay stamp duty, legal and removal costs.

Persimmon: part-exchange and double-your-deposit scheme.

Imagine Homes: mortgage paid for five years on investment properties.

Case Study: Helpful home exchange

When Helen Barraclough planned to relocate to Billingshurst, West Sussex, she did not hold out much hope of securing a quick sale of her home in Newton-le-Willows, Merseyside.

The 36-year-old teacher decided to move to the West Sussex town after getting a job at a local school. But before she could relocate, she needed to sell her home in the North. This was something of a dispiriting prospect because other houses for sale on her street were attracting few buyers as the market took a turn for the worse.

However, Barratt Homes offered a solution to the problem with a 100 per cent home-exchange package.

The housebuilder took the Merseyside home off Ms Barraclough's hands and assumed all responsibility for selling the property, allowing her to move in immediately to a new property on Barratt's Saddlers development in Billingshurst.

Ms Barraclough says: “Not having to worry about selling my house made the move much less stressful. Barratt also paid my stamp duty and the removal costs, which made things easier for me.”