Hi Qwerty,
I think you need to stop worrying about this.
To put it bluntly your only current choices are:
1) Stay on your current rate:
2) Remortgage, and possibly pay thousands doing so (Early Repayment Charge, solicitors, application fees)
a) and go for a Tracker, which would be cheaper now, and most likely equal in the next 12-24 months then more expensive in the last 3 of 5 years. so does it actually save you anything?
b) and go for a new fixed rate which might be cheaper based on the equity. (for every 0.5% is about £300 a year difference, or £50 a month) So would this be greater than the remortgaging costs?
A quick comparison on the main site will give you the offers and costs to apply for a new mortgage, you can contact your current lender for more information on the repayment (settlement) of your mortgage.
You already have the benefit of knowing how much your repayments are for the next 4/5 years, there isn't much certainty around anything else (other than mortgages are getting more expensive, and the BOE base rate will go up).
It is not certain that you would be offered a new mortgage, or one at the best rates.
I hope that wasn't too blunt, but you are wasting your energy worrying about something that you have taken a safe decision on.
Sparky.