I've been reading this thread with interest.
Probably going to get flamed for this....but why is the OP's dh being the bad guy here? It's being suggested that HE gives up his career to look after the baby. He's working long hours to support his family, is it so wrong that he wants his baby's mother to be around for their child?
Look...women have come a long way in the workplace BUT, rightly or wrongly, it's still the mother who does the lion's share of childcare in most cases, even if she had a good career before parenthood.
OP, working 4 long days when you can afford not to is a bit mad imo. Is there any possibility for you to job-share or work fewer days? If not, personally I would resign.
There is always another job round the corner but your baby is only small once, that's the way I see it. Feel free to disagree but I think if you have the chance to look after you baby you should take it. And (sorry) however good the childcare is, it's never as good as a mother at home. Even the most wonderful nanny won't love your child like you do. Don't mean to offend anyone, it's just my view.
My children are older now and we're busy with school/ballet/brownies/friends...lots of activities and running around. I would love to go back to the baby stage when the day was mine to do as I liked. It's an opportunity to take some time out. You say you haven't made any friends yet - whereabouts in Herts are you? I'm near Bushey. Have you found any local baby/toddler groups near you? Join the NCT? I'm presuming all your existing friends are working full-time so not available in the day?
Being at home with a baby doesn't have to be 'hard'. Hell, working in a highly-pressured job with a long commute is much harder imo. You'll find as your baby gets a bit older and starts doing more, you'll meet more people if that's important to you. I know it's a huge change but taking a career break to have a family is a positive thing. I've been at home nearly 10 years with my 3 and I don't regret it all. And I'm a bright, educated woman. I will go back eventually and will probably re-train to do something new which is exciting...but I feel lucky to have looked after my children myself.