Every Lender will have their own credit assessment system, none are completely the same. If your Bank offers Mortgages that is often a good place to start as you already have a credit history with them which will be taken into account. They will all search with a credit reference agency to see if you have any adverse information and confirm you are on the voters roll. Then go through your finances to assure themselves that you can afford the repayments.
Elley you need to have an employment history that shows you have been in a secure job for a good length of time. Looking at your recent posts it looks like you may have a problem in that respect, you have been asking about all sorts of jobs and self employment. Credit rating is only a part of the process of getting a mortgage, your employment history is just as important if not more so. 'Job Hoppers' stand no chance.