I may be wrong but I think the government advice has just been reversed on this, within the last couple of months. It used to be to avoid them whilst pg and bf, (whereas no other country advised this), BUT following an increase in nut allergies in children after a few years of British mums avoiding peanuts, it's now thought that avoiding them has caused increased sensitivity.
Countries where babies are weaned on loads of peanuts like Israel and African countries have practically no instances of nut alllergies.
I've been troughing sunpat with gay abandon since reading about this!