The ability to borrow at a reasonable rate, get an attractive mobile phone deal or pay insurance premiums monthly depends on your credit rating. Yet most people have, without realising it, done something that could damage their score.

Before accepting an applicant, financial providers want to be confident the debt or premiums will be paid on time and in full, and statistics show that people with stable, orderly lives are most likely to do this.

To help them judge who falls into this category, they give potential customers a score, usually between zero and 999, based on their application, any existing relationship and files compiled by credit reference agencies. Score poorly and you will be charged a high rate or rejected altogether.

Every adult who has ever had credit has a file, but only you and lenders you have applied to can see it. It includes information shared by current providers on your financial commitments and repayment history, together with any court judgements against you and details of previous credit applications.

According to RateSetter.com, 53 per cent of UK adults have unknowingly acted in a way that could damage their credit status. This could include something as apparently harmless as not updating the electoral register after moving house, or forgetting to close an account held jointly with an ex-partner.

Jay Magee, the lending website’s head of retail underwriting, said: “Credit scoring is an imperfect science, but it is a really important part of the decision of whether to give someone a loan.”

When lenders advertise, they must quote a “representative” rate of annual interest – formerly known as a typical rate. For cards, personal loans and hire purchase this is an APR, or annual percentage rate, while for mortgages and other secured loans it is an APRC, or annual percentage rate of charge.

Successful mortgage applicants must be given the advertised rate, but lenders are obliged to give the representative APR or APRC for other credit to only 51 per cent of those accepted. The rest can be charged a higher “personal” rate. However, this isn’t revealed until the paperwork is issued, so check it before committing to a deal.

Someone with a good score looking for a £5,000 personal loan over three years could borrow from Zopa, Hitachi or Ikano Bank at just over 4 per cent, paying a total of £148 interest. An applicant with a poor score might need to go to the likes of Lend Fair or Glo, who charge almost 50 per cent, increasing the interest bill to £3,700.

For credit cards, a borrower judged a good risk could get a card giving 40 months interest free on balance transfers, while someone with a low rating might be faced with a rate of around 60 per cent and no interest-free period.

Someone with a very bad rating could find it impossible to borrow from regulated lenders at all, forcing them to go without or turn to loan sharks.

Most people with a score this low will have considerable existing debt or a history of defaulting, but many with an average or poor rating will have damaged it unknowingly.

RateSetter.com says one in five have paid a bill late in the past five years, while one in seven are not on the electoral register, meaning lenders can’t confirm their identity and address. One in ten under 35 have moved house more than twice in two years, and one in fifty are still linked financially to an ex-partner.

While it isn’t reasonable to decide against moving house simply to protect your score, there are other things you can do.

A spokesperson for Tesco Bank said: “Customers can help improve their credit rating by checking their credit history, correcting any errors that might exist, paying all bills on time, and ensuring they are on the electoral register.”

If you have trouble remembering when bill payments are due, set up direct debits. If there is a choice about the sum, set it at the minimum and pay any extra you can manually.

Sever financial ties – including closing old accounts – with anyone who could damage you by association. Don’t attempt to borrow more than you can afford, and cancel unused cards or credit accounts to reduce the risk of looking over-extended.

Don’t apply for credit too often. Each time you ask, the provider will check your file. A record of checks remains for 12 months for others to see, regardless of whether you are accepted, and the more searches shown, the higher the chance lenders will be put off.

Bizarrely, some people score poorly because they don’t borrow. Mr Magee explained: “They think that by never getting into debt, they will automatically be seen as creditworthy. But, in reality, it’s by borrowing and paying back on time that you can build up a good score.”

The lack of credit history makes it difficult for lenders to assess an applicant’s creditworthiness. Taking out a prepaid card, which doesn’t require a credit check, can help with this.

Major referencing agencies include Experian (Credit Expert), Equifax and Call Credit (Check My File). Lenders use different ones, so if you have any doubts about your score, check a couple.

Most offer membership packages, costing between £4.99 and £14.99 a month, but there is no need to pay this, as you can view your file for just £2. This “statutory report” can be ordered from agencies’ websites.

Mr Magee said: “By checking your credit score, and taking a few easy steps such as getting on the electoral register, you can really improve your score and with it, your chances of borrowing more cheaply.”