Twiglett, I wouldn't encourage anyone to have anyone sterilised if they were not 100% sure as the reversal is not easy and there are very high failure rates of reversal.
Milupa. A couple of points. It can be done on the NHS and it is healthy (tho all medical procedures have an small eliment of risk).
No form or contraception is 100% except not having sex, or having a hysterectomy
Tubes can be clipped, clipped and cut, or, as happened to me, removed. The procedure is minor, you will be a bit sore, I had mine done when they delivered my ds by c-section.
But you should only have it done if you are 100% sure that you never want to have a child again, under any circumstances. What Zebra says is right, you have to be sure that even if the worst happened you wouldn't want to get pregnant again. I have 2 loved and wanted and planned children. But if, God forbid, anything happened to them I wouldn't want to be pregnant again, as I feel that I am too old (not making any comment about anyone else here) and I had too hard a time during my last pregnancy.