It will now allow applications for licensed HMOs of up to 10 bedrooms, an increase on its previous limit of six bedrooms.
The lender has also tripled its maximum borrower exposure from £1.5m to £5m, although the lower level will still apply to borrowers recovering from credit blips.
It said the changes were thanks to a new funding arrangement announced last week which included a £250m deal with JP Morgan, and that the moves demonstrated the intent to grow its buy-to-let business significantly this year.
West One’s current policy of accepting Multi Unit Freehold Blocks (MUFBs) up to 10 units remains in place.
West One Loans managing director for buy-to-let Andrew Ferguson said: “The exposure increase, in particular, allows us to support larger scale portfolio landlords with their financing needs across a range of products and we will be working closely with our intermediary partners to develop this market.
“Following so closely after the funding agreement announcement, it really shows how the business is making very positive steps with real intent to grow.”