There are many different things a lender will consider when you apply for a mortgage.
The obvious things such as your credit profile, and proof of income are always important, but we find that is in other areas, not immediately obvious to our clients, that applications may be declined or delayed.
Lenders will normally want to see your latest three months bank statements as part of their underwriting assessment. They want to see that you maintain your account in good order, meaning that you keep your account balance ideally in credit, or at the very least, well within any pre-agreed overdraft limit.
If your bank statements show evidence of unpaid Direct Debit Mandate or unauthorised overdraft fees, this can lead to an application being declined, as it indicates you are not managing your finances satisfactorily, and lenders can see this as a sign you may not be able to maintain your new mortgage payments, particularly if the new mortgage repayments are higher than your current rent payments, or you are living with friends or family and not party to a rent agreement.
Another matter which cause issues with an application, are recent late payment profile on unsecured credit accounts such as unsecured loans or credit card accounts.
Although some lenders will accept the odd late payment on unsecured credit accounts, being currently or recently in arrears on a number of different accounts can be a problem.
You should try to maintain all unsecured credit accounts wherever possible, and bring any accounts currently back up to date ahead of proceeding with a full mortgage application.
Finally, you should avoid taking out any payday loans or other forms of short term lending, close to making a mortgage application, Lenders will decline an application where there are active payday loans or have recently been, payday loans in place.