The move comes after brokers told Keystone that they were increasingly looking to complete mortgages on multi-unit apartment blocks and high value multiple occupied properties.

Previously Keystone capped its loans per property transaction to existing landlords at £350,000.

The Aldermore-backed lender has also introduced a minimum loan amount of £50,000 but will also consider strong applications that do not meet its new criteria. Keystone products are offered exclusively through broker Mortgages for Business.

David Whittaker, managing director of Keystone Buy to Let Mortgages and Mortgages for Business, said:

“One of the reasons for launching Keystone earlier this year was to meet the needs of professional landlords who have been underserved by the mainstream buy to let lenders in recent years.

“Upping the maximum loan amount clearly demonstrates that we are able to respond quickly to investors’ on-going requirements in order that they can expand their portfolios at a time when housing is in desperately short supply.”

Rob Lankey, managing director of commercial mortgages at Aldermore, added:

“In a short space of time the brand has cemented its position as one of the main go-to lenders for professional landlords.

“It has already produced in excess of £20m of mortgage offers and this criteria change and the fact that our five year fixed rates are now only 0.25% more than our three year rates, will encourage more brokers to recommend our products to their customers”.