Every time you want to borrow money, such as a mortgage, credit card, loan, or mobile phone contract etc, the lender will look at this score when making their decision to approve your application. Once you have credit, the activity on the account is monitored and communicated to the credit reference agencies; this information is used to create your credit score. The better the conduct of the account, the better the score.
Where you have a low credit score, it could indicate you have had issues paying credit on time or even worse you have defaulted on accounts or have been issued County Court Judgements. It could be something less serious, but it is really impacting your credit score and ability to get a mortgage.