Xenia is right about most nannies, it may be the case that you can find one who is doing some part time course.
One odd thing about the nanny market is that salaries are quoted in terms of what she actually gets in her hand, leaving you to pay all the tax.
We use NannyTax, they make it less hassle.
I guess you'll be paying out around 400 per week, but there is quite a variation, and do not believe the crap about nanny wages you see in the media which is about as accurate as BBC Science coverage.
Horizon
We also let DS "interview" them. He asked penetrating questions like "what is your favourite colour", and "do you want obe our nanny",m and measured them a la Mary Poppins
What was interesting was that several failed this test...
When confronted with a bright, polite yet pushy child they clearly felt awkward, a couple just when "ummm errr".
One turned up on our door visibly suffering since the walk up our hill "nearly killed her". Fitness/weight issues do seem to afflict nannies more than the average person as far as we can see.
Some agencies were very sniffy about the fact that we didn't live in Kensington, and we did pick up the idea that because we live in Essex they felt we'd be pathetically grateful for anything they sent. We found that it helped to mention our job titles, even though of course it is largely irrelevant to the job.
Part of our spec was an "educated" nanny, we didn't demand a degree, though we've ended up with 2 graduates and that's worked well for us.