Always check your credit files before applying for a tenancy to minimise the risk of rejection. You have a right to see your credit files for £2 but can do it for free and should do it regularly. Check EVERY detail; people have had applications rejected because an unused (but not cancelled) mobile contract’s address had not been updated after a house move so be vigilant. Look out for entries on your record that aren’t yours – they may be a sign of ID fraud.
More information on how to check your full credit report for free can be found here