Firstly let me say that I am not qualified to give financial advice etc. :)
What decides if it’s worth doing is a combination of:
[*] the difference between interest rates on your savings (net) and the rate that you’re paying on your mortgage
how long the mortgage has to run
the amount outstanding on the mortgage[/*]
So without knowing the precise figures it’s hard to say.
My personal view is that it’s worth paying down as much of the mortgage as you can afford as soon as possible as long as the mortgage rate is greater than the net interest on savings. Apologies if I’m teaching you to suck eggs here but in the early days of the mortgage you’re paying mostly interest (assuming a repayment mortgage) but as time goes on each payment pays more capital. So any overpayment will help reduce how long you’re paying the mortgage for, which has to be a good thing!
So overpay as much as you can afford as long as you have an emergency fund to cover major events such as loss of job, new boiler, car repairs, wanting some shiny bits for your bike etc.