It was a lot more straightforward for me with EBS years ago - I just increased the monthly repayments above the "normal" level dictated by the capital sum, rate and term and the excess went against capital immediately. I also did lump sum repayments of arbitrary amounts along the way. However I guess it depends on the terms & conditions of your specific loan agreement. On the other hand, under the Consumer Credit Act, no lender can penalise/charge an owner occupier for making capital repayments off a variable rate mortgage on their PPR.