If you're 45, you could get (technically) a 25 year mortgage, which would make your monthly amount lower. You've likely also built up more equity since the 5 year fix was taken out. I would speak to an IFA, they would be able to give you all the options. It could be that any repayment charge to break the 5yr fix could be saved over the course of the new deal.
We are looking at a 31 year 5yr fix term (I'm 38) and even with the repayment charge and moving from a 2 bed flat to a 5 bed house, our monthly payments will only be £100 more than they are now.
I had to get it out of my head that getting a 31 year term doesn't have to mean paying a mortgage until I'm 70. We can move or overpay and get a different deal in 5yrs, and later moves are likely to be out of London or to a smaller place, which would pay off the mortgage.