SERPS is the governement scheme for a pensiion above and beyond the state pension. It is not really taxation as it is voluntary. You will not be missing out on your state pension because of SERPS the two are entirely separate. The state pension you get depends on the number of years NI you pay, for a full state pension you need, I think these days, 30 years worth. SERPS is irrelevant to that.
I know a bit about SERPS but don't understand your question and was going to ask for clarification. However it seems it may have been answered to your satisfaction now. Let us know if you need any further info on this.