I don't think you have to give up your career at all, I think that working mothers in the UK have lots and lots of flexibility, and yes childcare is expensive, but you can get some help with that with things like Childcare Vouchers (which are taken out of your paycheck before taxes) Yes, its a sacrifice, but its worth it for us, and to be honest, I love being a working mother and even though I am on maternity leave (for a year! Hooray!) with my 10 week old right now, I feel a bit of a loose end and I miss the structure that working give my life.
There are lots of childcare options, for instance, Childminders are less expensive and more flexible than nurseries are, although nurseries are very social, and you will get some help when your kids turn 3, they get 20 hours of free daycare a week (athough with the new government, who knows if that will stay or go)
One big plus for me is that due to a some kind of European legislation, because I was getting childcare vouchers while I was working, and I didn't opt out of them, my company is obliged to keep paying them for my maternity leave, so while I am home with my new baby, my 4 year old son is still with the childminder.
In all honesty, we could afford to have me stay at home with the kids as my husband does make a good salary, but I like working, I like having my own money and I enjoy the lifestyle of being a working mother!! Don't listen to anyone else, do what feels good to you!