Dilly - I employed a nanny for 2 years who had a similar job description to the one you're proposing. I advertised it on gumtree, making it clear that there were some house responsibilities whilst dd was at nursery. We found a FABULOUS girl, who was from Slovakia but engaged to a local lad. She was amazing so we increased her pay twice. Initially we paid £7.50 ph gross, then £8.50, then £9. Plus, she got us to fire our cleaner, who was rubbish and charged £10 ph, and she did it instead also for £10 per hour. Although we no longer need a nanny, we see her loads as a friend and for babysitting, we went to her wedding in Slovakia, etc.. When she left us she went to friends of ours.
So what you are offering is totally realistic, ime. I would advise offering the job initially at a lower hourly rate, with space to increase it, making clear to the nanny that you will do 6 monthly reviews and the money is in the pot to increase. So perhaps starting at 8.50ph gross. I know our former nanny still earns £9 ph, and she says she doesn't anticipate getting any more than that anytime soon, as none of her nanny friends earn higher than that. So £10 per hour sounds a bit high, esp in Dorset (we're in Oxon). I have a housekeeper now, (well 2, who job share) and I pay £11 per hour gross, for a much harder job.
Good luck in your search - I'm sure you'll find a lovely nanny!