Do you have any other savings ?
Reducing your mortgage saves a lot of money, but it is a very long term savng strategy, and it is very hard to unlock the savings if you ever need the money. If you ever need the money, you will have to ask the bank for a remortgage and they might say no.
If you are lucky enough to have money to save, thnk about three types of savings
1) short term savings - holiday, emergency house repairs, big medical bills etc
2) Emergency fund - what if you lose your job, what if the car breaks down, what if the roof comes off the house
3) Medium term / long term savings / pension
if you have 1 and 2 sorted, think about 3. There are lots of different saving/investment stratagies. The best one will depend on your age / pension provisions etc. If you are a permanent semi-state then, you probably have a decent pension plan.
It reallty depends on what you think you would like the money to do for you (income now, lump sum in 10/20 years).
do you think you will want to do an extension to your house, when you have kids or when the kids are older ? if so, put it away for that.
if you decide what the money is for, the strategy will be clearer.