Have you checked out other financial support that you'll be entitled to once DC is born? You should get tax credits and also child support from your DC's father (unless he's not alive, not known or uncontactable).
Tax credits will give you quite a lot of your income is low-ish and your childcare costs high, and it tapers off for the more you earn. What this means is that if you earn more you have slightly more to live off, but not a lot more. So it can be really worthwhile considering if you woud be almost as well off working part-time. Tax credits also gives you a small (around £10/wk) boost for working 30 hours or more, so working 4 days a week could give you almost as much money as 5.
Child support is usually 15% of the ex's net income for one DC, unless he's on benefits when it's just £5 a week. But if it's a possibility, work it out and factor it in to what you can afford. MrsBig is right to suggest looking into what your DC's dad can do in terms of childcare too. If he's on the scene at all, and potentially capable, then use him.
I went back to work when DD was 9 months old - it's not a bad age to start leaving them as they tend to get more clingy by a year or so, so good in some ways to start earlier. But I only worked 3 days a week, and really did value the two days a week I had at home with the DCs (DS was 4 at the time). You can manage with full time work, but personally I think if you have the choice it is nice to have some more time at home with them.
Also, spend the 9 months maternity leave building up your contacts with other mums - there's heaps of opportunities to do this via baby groups, toddler groups, etc. Even with formal paid full time childcare in place, you'll always need something to plug the odd gaps when the childminder is ill, you need to work an evening, or something else crops up. You can offer to have their DCs round in exchange (though this too is easier if you don't work f/t - though I guess you could offer weekend playdates)
And don't be afraid to ask for flexible or p/t working if that is what you would like. You've a legal right to have it considered (if you've been there two years or more I think). They may be quite happy to have you work from home a little, or reduce your hours. It's ever so common for women returning from maternity leave to ask to go part-time or vary their hours a bit - employers will hardly be surprised by it. The worse they can possibly do is to say no, so don't hesitate to ask.
But if they say no, and you have to stay full time, don't panic. You'll be fine - as suggested shop online, rope in whatever friends, family and babysitting support you can get, and if you can afford it, get a cleaner for an hour or two a week.