I left the UK at 33. I paid in Class 2 NI contributions for myself and my husband and we now both qualify for full UK state pensions. The age at which they will be paid has increased, but it's still an absolute bargain and now at age 60 I fully appreciate that. For me, it's the cost of a couple of bottles of wine in a restaurant per year ... would get you a few more beers though!

I was told by HMRC that for the the years I'm missing from 1993-96 (when I was a mature undegraduate) I'd have to stump up 8k to get and extra fiver a week state pension, I wondered if this was a miscalculation on their part as it seems an awful lot of money.

I believe it's a mistake. 4 years would be less than 1k assuming you left the UK to work in CH.

I'm planning to look into it again as HMRC have also given me 2 conflicting pension forecasts. One says I was contracted out of SERPs and the other says I wasn't, the difference between the amounts on the first and second letter are about £20 a week I think. The letters were sent out the same week arriving within 3 days of each other.

Where did the SERPS contributions go?

Your guess is as good as mine. My accountant back in Scotland looked into it and she said she didn't believe I was contracted out because of the dates involved.