Are you looking at buying through an agency? They will be able to inform you of any protocol.
I found this good article in
the Times :
http://www.timesonline.co.uk/tol/money/ ... 007950.ece which might be helpful.
You will also need to announce your arrival with your local authority in France - I'm not sure of the specifics, but the local
mairie is usually the place that sort of thing is done, and if not, they will be able to advise you of where to go. Their details should be online and I would imagine it would be best to call in advance once you have chosen your property.
It's also a good idea to get together with the neighbours. If you will be living in a town, drop invitations to an early evening drinks at your house to a dozen local properties, if you are in the countryside, maybe you could bake some English biscuits to drop in on your neighbours "just to say hi". As expats it will make it easier to make friends, and you can then ask for advice on the best value local supermarkets, brasseries or rubbish collection days.
I get the impression that a fair few foreigners settle in Brittany, so I would imagine that it shouldn't be too difficult.