Try
http://www.farmstayuk.co.uk
Covers the whole of the UK and offers self catering, b&b and guest house accommodation at some of the most stunning locations anywhere.
You can be near towns or off the track , by the coast or up in the hills, have your own river beat or a private beach.....Search an area you fancy and just book direct with the accommodation.
Plus if the farm allows you can get to help - handy to keep the kids busy - and in any case you'd be guaranteed the freshest of breakfasts and if staying SC, be able to take advantage of the local food so really get to have a good, quality stay.