The lender has reduced the buy-to-let affordability rate from 6% to 5%. The affordability rate is the notional interest rate Santander uses to calculate how much rent a borrower needs to achieve to service the loan.

The minimum gross rental income requirement remains at 125% of the mortgage payment.

So a borrower with a mortgage of, say £100,000 would need to generate annual rent of (£100,000 x 5% x 125% =)£6,250 to cover the loan, rather than (£100,000 x 6% x 125% =) £7,500.

Santander will also increase the maximum loan size per property from £500,000 to £750,000 from Friday 27 September.

Santander for Intermediaries director of retail assets Phil Cliff said:

“The buy-to-let market has seen strong growth over the past couple of years and we are keen to increase our support of this market. We are therefore delighted to be announcing enhancements to the lending criteria for our buy-to-let offering.”

Applicants must already have a residential or buy-to-let mortgage. At least one of the borrowers must be employed and earning over £25,000 per annum. Houses for multiple occupancy are not eligible.

Santander is also launching a range of two-year residential tracker mortgages available up to 90% loan-to-value, with no early repayment charges.