If you are looking for a Nanny, or are a Nanny looking for work then I have found a good website. Its called www.nannyadverts.co.uk It is new so there isnt many ads. of yet.
Also these are also good:
www.nannyjob.co.uk
www.nannydirect.co.uk
www.nannynet.co.uk
www.bestbear.co.uk
www.nannyselect.co.uk
www.mynannynetwork.co.uk
Hope you find these sites of use