Just to add, whilst its lender specific a general rule of thumb is 1% penalty per year left when on a fixed. But some lenders keep a high value for full term
So if you have 2 years left its quite likely the penalty would be 2% of any overpayment.
As others have said its not worth overpaying on your mortgage in that case.
Bear in mind tax on savings £1k for 20% income tax payers, £500 for higher, £0 for top.
Could be worth moving it into an ISA as opposed straight savings if you will suffer on interest.
If your saving early then you can lump sum the payment on your anniversary date. Its an annual allowance the extra you can pay so get in as early as possible.