Credit files crammed with our personal and financial data have never been so important in deciding whether we can borrow money.

The credit crunch and lenders' subsequent aversion to bad debt mean that our financial histories are being placed increasingly under the microscope. Missed mobile phone payments or an unsettled mail-order account might have been overlooked a year ago, but now mortgage lenders consider these details to be much more significant and may use such misdemeanors to reject applications.

There are three main credit reference agencies in the UK: Experian, Equifax and CallCredit. These collect and share information about individuals with companies that offer credit agreements, from banks and building societies to mobile phone providers. It is added to information from public records such as the electoral roll.

The rising number of rejected applications for mortgages and credit cards has fuelled a 25 per cent increase in the number of consumers checking credit reports online in the past six months.

Chris Carcon, 28, of Aberdare, South Wales, is typical. He checked his report after being rejected for a mortgage recently. “I was surprised at the amount of information on there, and how far it goes back,” he says.

After being rejected by one lender, Chris was told that a missed payment on his credit card was to blame. He was encouraged to reapply after five months, when his credit score would have improved.

Even more information is set to be handed over to agencies so that companies can better decide whether we are creditworthy. At the end of this month Apacs, the UK payments association, will announce plans for credit card providers to share “behavioural data”, including the number of cash machine withdrawals and whether customers make only the minimum repayments each month.

Door-step lenders will also be submitting information to credit reference agencies for the first time from next month. The details of two million loans, typically made to higher-risk consumers at high rates of interest, will be added to the records of the three reference agencies, under the orders of the Competition Commission.

It doesn't stop there. Discussions have also begun between the agencies and utilities companies, with the aim of including information about customers bills and payment history on credit reports. Equifax says that the earliest that these details could appear on your report is next year. Council tax payments and local authority rental histories could also be included soon.

All three agencies have to provide you with a copy of your credit report for a fixed price of £2, available through the post. The companies also offer online services, which are charged by subscription. These allow you to download your credit report and include an e-mail or text service to alert you to any changes on your file. This is particularly useful if you are concerned about identity fraud.

CallCredit Check is the cheapest, charging £12 a quarter. CreditExpert, from Experian, is the most popular online subscription service. It costs £6.99 a month, but you can have a free 30-day trial. Once you have subscribed, you can also pay £5.99 for a credit score, plus a guide on how to improve your score.

How to read your credit report

1 To obtain credit, a lender needs to be able to link you to a permanent address on the electoral roll. If you have not registered with your local council, it is likely to damage your chances of getting credit at a competitive rate.

2 Having a joint account or jointly applying for credit with someone means that his or her details are attached to your file and remain so indefinitely. This can affect your credit score.

3 Court judgments, showing that you have been taken to court for non-payments, bankruptcies and individual voluntary agreements, stay on your file for at least six years. If you settle a court judgment, make sure that this is added to your report.

4 Credit account information includes the lender, the type of credit and details of the agreement. The status history charts repayments for the past 36 months. The code “0” means that payments are up to date; “6” means that they are late by six months or more. James Jones, of Experian, says: “If you close your account, missed payments remain on your report for six years, but if you keep the account open, the missed payments are removed after three years.” Overdrafts, credit limits, promotional rates and balances are also detailed.

5 Repossessions, accusations or convictions for fraud, plus details from the “gone away network” - a group of lenders that share details on borrowers who owe money but have absconded - are also included.

6 Previous searches by lenders, called footprints, show all recent applications for credit and stay on your account for 12 months.