sterlisation in the uk

does anyone know the likelyhood of being granted to be sterilized and the process of going about it? I have recently had two premature babies born due to pprom in both pregnancies and the doctors cannot do anything to help me if I decided to have more children in order to prevent it happening again especially earlier in the pregnancy . both children were born with low blood sugar and quite large for their gestations . so im.now waiting to get tested for type 2 diabetes myself in a few weeks. ive just recently had the mirena put in a few days ago but im looking to be sterilized. both myself and my partner have agreed we dont want anymore children and I do not want to risk future pregnancies resulting in a loss and im happy with the two children I have. does anyone have any input? as its not advisable for me to have anymore children as im now considered high risk