When you apply for credit the success of your application will be based on a combination of the personal information you provide on your application form and a credit report provided by at least one of the three credit reference agencies operating in the UK (Experian, Equifax and Callcredit).
This encompasses details of how you run your finances including any defaulted or late payments, CCJs and bankruptcies. While CCJs and bankruptcies adversely affect your credit score for a period of six years, the effect of defaults lessens over time with good financial practice helping to cancel this out.
Finding your file
It's possible to access the credit files Experian, Equifax and Callcredit hold on you and is advisable to check them every 18 months or so as this will ensure any mistakes or fraudulent applications are identified and amended. You can either obtain these by post (for £2 each) or via the internet.
In order to access your reports online you may be required to sign up for a pay monthly access scheme. These are really not necessary and thankfully most come with a free trial that allows you to sign up, obtain your credit report and then cancel before any money is debited from your account.
If this sounds like too much effort (or you're one of the many who often forget to cancel subscriptions after a free trial), you can purchase a summarised report comprising data from all three agencies from CheckMyFile.com; this does come at a costs but is much cheaper than any of the pay monthly plans offered by credit reference agencies.
What you should check
Once you have obtained your credit report you should carefully check that all of your details are listed correctly focusing on both your current and past debts, repayment history and personal details (as these too impact your credit score).
If you do notice any errors you should contact the agency directly and ask for an amendment to be made as any mistakes could impact your ability to get credit. In most instances the credit reference agency will be able to resolve this, but if there is a dispute you may be referred back to the lender in question. If they refuse to amend your file you do have the right to add a notice of correction explaining the error to future credit providers.
By regularly checking your credit file you will be able to identify any mistakes or fraudulent applications made in your name, protecting your financial integrity so that you won't be unduly turned down for credit when you need it.