The amount was raised after feedback from brokers revealed that many customer enquiries were for higher value HMOs and multi-unit freehold blocks.
The change will help investors to continue growing their portfolios with Keystone which, unlike some lenders, does not impose a limit on the number of loans that can be held with the brand.
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.”
At the other end of the lending scale a minimum loan amount of £50,000 has also been introduced although for particularly strong or worthy applications exceptions can be considered.
Keystone Buy to Let Mortgages, which was launched in April, is fully funded by Aldermore Bank and offered exclusively through Mortgages for Business.
Rob Lankey, managing director of commercial mortgages at Aldermore, said: “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 £20 million 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.”