All mortgage lenders will look carefully and in detail at your credit score before making a lending decision, as this shows how responsible you are for managing your personal finances.
They will use your credit score, along with your annual salary and personal details, to work out how much of a risk they think it is going to be to lend a large amount of money to you. The stronger that your credit score is, the better your chances are of getting accepted for the mortgage that you applied for, and the more choice of lenders you will have to choose from.
You also need to take into consideration any oversights, such as not being registered on the electoral roll, or failing to close down credit card accounts that you don't use anymore. Although these seem like small things, they can have a negative impact on your credit score and ultimately affect your chances of securing a mortgage.
Before applying for any mortgages, you should always check your credit score carefully to see if there are any particular reasons why your application could be rejected.