The affordability criteria used by most credit reference agencies is the total household income should exceed 2.5 times the rent. So if the rent is £1,000 per month then total household income should exceed £2,500. If there are 2 people renting the flat (household) and they both earn more than £1,250 then they will pass the affordability criteria. Proof of income should usually be in the form of the last 3 months salary slips.