A fulltime nanny (aka, daytime, approx 9-10 hours, not live in) is only going to run you about 25-35k in many areas of the country. (I'm speaking of a legal resident with a green card or US citizen).
I think you'll find buying a smaller home or going on fewer vacations or eating out much less and getting some domestic help will drastically improve the quality of your life.
This is true, and is basically what I pay my nanny. I clearly could not afford to do this if I worked in a less lucrative industry. In that case, I would most likely stay home.
Sounds like you're not making enough to make living/working there worthwhile. Try a cheaper city. I'm not talking Topeka, but do look at cheaper cities with a tech scene. (I'm a big advocate of Atlanta, and live here, but Austin also works nicely).
Or just get a new job in the same city with better pay.
Edit: Oh, I see you're in the UK. That is quite different. Try pointing that out. The UK has several high cost areas and lower cost areas as well, but I know little about the tech scene.
The solution may be "Dude get's higher paying job"
I earn the going rate for a PHP developer in my area, in a job that I love that's close to where I live. Unfortunately it's a fairly low-paying area, so although I could probably squeeze another couple of grand out of a different employer, that would be eaten up by travelling costs/etc.
If money were the issue here, I'd just go up to 5 days a week.
Yeah, honestly, increasing income, or your hubby stopping some work is probably the better directions. In the states python/ruby web dev pays a bit better than php, so perhaps you could try moving towards that.
My gut says 'Don't buy this house, it's the wrong size for your income/family situation and in a place that doesn't pay well enough for the life you want.'
Jem, you can find a nanny for less than you think. There are lots of young ladies out there with out jobs who live with their parents and are much more the family type than the career type. Those girls would jump at the chance to take care of your son and don't cost very much, probably comparable to what you are paying now.
I think you'll find buying a smaller home or going on fewer vacations or eating out much less and getting some domestic help will drastically improve the quality of your life.