Had you even discussed this before getting pregnant? My husband and I are TTC and we've already discussed what the plans are WRT to childcare, hours, returning to work, shared bank accounts and the like. So we're already on the same page. No way would I drop the bombshell that I wanted to be a SAHM after the baby was already here.
I do get your feelings, I really do. I want to be a SAHM as well, but please don't give up work without some kind of financial protection in place. Giving up work as a single woman (as legally, you're single) is extremely risky. You're not paying into a pension, earning your own income and are going to be completely reliant on your partner. What if, God forbid, he gets injured and can no longer work, or dies? It does happen. You won't be entitled to widows' allowance, you probably won't be entitled to his pension either.
Even if you look at more likely scenarios - what if he loses his job and decides to do a runner? What if you break up? How are you going to support yourself as a single parent who hasn't worked in 3 years? Or 5 years? He'll only be liable for child support - he has no obligation to support or house you.
Please if you do this, consider getting married. It only costs £200-odd down the registry office, but it gives you a massive amount of protection as a SAHP. I would never even consider giving up work if I wasn't married - in fact, it was a prerequisite to having children for me. No unprotected sex outside of marriage (even though we lived together and were engaged) because I needed that legal protection in place first.