Don't forget in addition to NI contributions in the UK the majority of those living in England who worked are also charged a substantial sum for items on a prescription - in excess of £7 each item.
National Insurance contributions are not negotiable - other than a reduced contribution rate if you are in a private pension scheme. If however you choose, or your employer provides, private health care you still have to pay towards the NHS. Ahmet drew a similar comparison when I went with a friend into the Consulate Office in Fethiye the other day. He said he has private medical insurance but still has to pay Bag Kur.
Yes, it is 3 months out of the UK as we found when we had a letter from our GP telling us they were removing us from their lists as they believed we were now residing outside of the UK.