My payments have dropped £175 in the last few months, so I went into the local Barclays and they just accept cash amounts from me and it gets taken off the balance next day.
When rates where high it might have been worth putting the cash in an account and saving up the interest, but really whats the point when rates are so low…pay it off now and get the bills down for the future.
Most trackers tend to have unlimited amounts, fixed etc tend to be 10% of mortgage balance without any penalties.
If you pay off £100 per month extra its worth around £1400 when you chuck on the interest saving