RBS forcing BTL mortgages onto repayment basis

Just got back from dealing a BTL portfolio deal in Salford, Lancashire,  nice grup of BTL properties and the current lender RBS is being difficult and insisting the landlord changes them all to repayment,  not too sure why RBS is insisting tat some of its BTL mortgages move from Interest only to repayment,  but not complaining as they keep sending customers to us, that want help and advice about how to remortgage away from the RBS mortgage repayment requirement and refinance the BTL’s onto interest only