The medical evidence is quite clear - reversal of sterilisation is sometimes successful. In cases where the reversal procedure is not successful then some form of fertility treatment can often achieve a pregnancy. But PCTs don't decline to fund reversal of sterilisation on clinical grounds.
PCTs are not obliged to fund reversal of sterilisation, and most of them don't. All PCTs will consider individual cases, but a case would have to be very exceptional indeed for a PCT to fund reversal of sterilisation when someone voluntarily made themselves infertile.