As MrsTM says, it is all dependent on the terms and conditions of how Abbey will treat the 'savings pot'...
I would also shop around and be careful of mortgage protection - there are so many stories about how customers have been let down and policies not covering the conditions you would think would be fairly standard under the protection ..
On the other hand, if you do have a bit of spare cash at month end, you can't really go too wrong if you use the cash to put it towards paying off the principle mortgage amount ... the smallest figures add up and do cut the overall cost