The updated fee structure will replace several ad-hoc mortgage services fees that used to be in place for the brand.
The fixed price of £275 will cover the set-up, maintenance and closing down of the account and will be debited to the mortgage account on completion.
It will then remain interest-free for the rest of the loan term.
The mortgage account fee will apply to any new mortgage where the first KFI is generated after 12pm on February 21.
The online application system will be out of use between 8am and 5pm on February 22 while updates are made to take account of the new charge.