Having read on another thread ("Paying Nannies when sick") gripes from UK nannies about jobs going to girls from accession countries who will work for less, (and do more in the way of housework), is this not just pushing the market rate down for qualified/experienced nannies?
I am not in UK, but I would look at it as providing more affordable childcare, provided you can find someone trustworthy and reliable. I lived in UK briefly about 4 years ago and a nanny friend of mine was earning GBP 25,000 and got a flat thrown in with it. This is more than I was earning at the time and could never have afforded this sort of money for someone to look after my children.
I am not suggesting slave labour from Central European girls, or paying them an au pair's "pocket money" for what is essentially a nanny job, but paying them a reasonable wage and providing free accommodation means that a lot of people, who could not afford a nanny or nursery fees, will probably be able to get back to work.
Of course, there will always be those who want a Norland nanny and can afford one, but it seems to me that your average Mum would welcome these Central Europeans with open arms...
I'll run and hide now...