I think their decision was influenced by the most recent budget. With business costs rising due to the national insurance increase, banks are anticipating that inflation will fall less quickly, as costs could be passed on to consumers. This is compounded by government spending increasing which also has the potential to have an inflationary effect.

Given this background it is not inconceivable that BoE might need to raise interest rates again and this means the banks need to keep their fixed rates high to cover the risk of people locking in rates that turn out to be too low.