The lender previously only offered a maximum of 80 per cent. The loan is available from 1.75 per cent over Bank of England base rate for full status loans, which gives an initial rate of 5.75 per cent.
The product is available to finance an unlimited number of properties up to a maximum total of £1million.
Roger Hillier, product development manager said: "Increasing our LTV to 85 per cent confirms our commitment to the buy-to-let market by making it more flexible and less complicated. The mortgage retains the popular features of ourexisting, award winning buy-to-let mortgage, with the additional benefits of an increased LTV and streamlined pricing."