If you are one of about 400,000 homeowners who have managed to take out a mortgage between January and March this year, you should count yourself lucky.

This time last year that figure was 503,000, according to the Council of Mortgage Lenders. Now the forecast is for the number of mortgage approvals to continue to fall, as a unique and unprecedented cull begins to hit borrowers. A year ago there were 10,438 mortgages to choose from for prime borrowers. Moneyfacts.co.uk, the financial website, says that there are now fewer than 2,400.

The story gets worse. Not only are there fewer deals on the market, but the deals that are still available, with only a small handful of exceptions, are thousands of pounds more expensive over the term.

It is not only cash-strapped first-time buyers and the credit-unworthy who now face a struggle. It is all of us, even the most sensible. As if to prove the point, NatWest raised the cost of its variable-rate offset deal - the most popular home loan for more affluent borrowers - this week by 0.2 percentage points to 6.45 per cent.

Moneysupermarket.com, the comparison website, has calculated that, since 2006, the average increase in the cost of a two-year fixed rate from the five biggest mortgage lenders is £1,224 over the two years.

Rob Clifford, chief executive of Mortgageforce, the broker, says: “Clearly, even those who have no worries about being stranded high and dry with no mortgage available, still face a price increase. This payment shock could be as much as 30 per cent.”

All of this adds up to a much higher cost of home ownership for hundreds of thousands of borrowers who are either due to remortgage or are considering buying. But will you be one of them, and what can you do? It all depends on what type of borrower you are.

Prime

The most at risk of having restricted or no choice of alternative lender are “heavy adverse” borrowers who have had many county court judgments (CCJs) or defaults. But borrowers who have perfect credit histories could also be high risk. This includes people with unusual property types, such as concrete construction, wooden frames or tower-block flats, as well as those who look less stable in the eyes of lenders, including foreign nationals or freelance and contract workers, people with little or no equity, the newly self-employed or anyone who has recently started a new career.

Those with the widest choice of deals are people who have plenty of equity in their homes or significant deposits. So if you have some spare cash, it is worth overpaying on your mortgage if there are some months to come before you have to remortgage, as this will improve your chances of getting the best deal. Melanie Bien, of Savills Private Finance, the broker, points out: “Most lenders allow you to overpay by 10 per cent a year without penalty.”

The other thing to do if you are in a safe place with your mortgage and want to stay there is to make sure that you keep on top of your finances. “Pay your bills on time,” Ms Bien says. “Lenders are looking for clean credit histories, so it is essential that you pay on time. It is also worth checking that your credit file does not have any incorrect entries before you remortgage or take out a home loan for the first time.”

Sub-prime

If you have had credit problems in the past, you are now in the worst possible position and will need help.

Speaking to a broker is your best bet because he or she will have access to all the deals on the market and

will be able to help you to work out whether you are sub-prime or could qualify for a prime deal. Some brokers, including London & Country and John Charcol, are fee-free. Ms Bien says: “With far fewer sub-prime loans available, it may be hard to find a competitive deal. Consult an independent broker with access to the whole market to see whether a sub-prime deal is your only option and to help you to find one.”

Also, ask yourself whether you need to buy. If you have missed payments in the past and have CCJs against your name, you are regarded as high risk and may struggle to find a loan. If this is the case, it may be worth delaying your purchase until you have repaired your credit rating.

First-time buyers

This time last year there were 1,530 mortgages available for loans above 95 per cent of a property's value. Now there are only 430. For aspiring homeowners this means one thing: save a deposit. Ideally, you need 10 per cent to be certain of a reasonable rate.

Ms Bien says: “With house-price growth slowing, or even falling in some areas, there is less of a danger of being priced out of the market while you return to old-fashioned values and save for a deposit.”

If you want to take advantage of falling prices to get on the property ladder now, speak to your parents. If they can't help with the deposit, they may be able to act as guarantors. This entails them guaranteeing to pay your mortgage if you default, which makes you less of a risk to the lender.

Buy-to-let

Landlords who need to remortgage are being advised to act fast. Several lenders, including UCB Home Loans, are increasing the minimum deposits they require to 25 per cent. Lenders are also tightening their rental criteria, so if you need to remortgage, do so without delay.

Another thing to consider is how to maximise rental income. Rents have increased in recent weeks, so make sure that you are charging tenants enough. Ms Bien says: “Is each property working as hard as it should be to earn you as much as possible? For example, can you convert a large lounge into a smaller lounge with another bedroom?”

CASE STUDY: Repayments up by £250 a month

Barry Anderson and Claire Lewis, of Surbiton, Surrey, will pay an extra £250 a month when they remortgage on their two-bedroom flat in July. The couple, left, will switch from a tracker mortgage charging 0.38 percentage points below the Bank of England base rate to a deal 0.49 points above base rate, with Lloyds TSB Scotland.

Their broker, Savills Private Finance, advised them to book the rate in advance in case it increased. The rate went up the next day. Mr Anderson, an accountant, says: “We will be paying a lot more but in a way we are lucky because it could have been a lot worse. We won't have to cut spending, but the higher rate means that it will take longer to save to move up the ladder.”