Hi someone mentioned welcome cottages before and we have used them several times with our doggie - there are lots in the Lakes that take dogs and I have never been asked about the size or breed by any of the owners as you book through the agent and they just expect you to have a well behaved dog. We stayed at a nice cottage in Heskett Newmarket north lakes for instance. We have also stayed in their cottages in Cornwall, Shropshire and Powys - all fantastic walkies and Scotland - where most pubs and inns allow dogs in which is good for eating out with a pet in tow. The only place we had a problem finding dog friendly places was York for some reason cities and larger towns can be a bit anti-dog. The National Trust also do some cottages (which can be more pricey) but dogs are allowed in some of their properties too.
We tend to find that in country places they accept dogs more and often so long as your dog gets on with the pub dog, the farm dog and the cats, hens and other beasties there is no problem.
Ultimately if you have a socialised dog who is well behaved you should be able to get in. The dog proves to be a real ice breaker as well we definitely have met more people thanks to the pooch.
I too worked for the NCDL once and I know they were trying to plug dog friendly places. And the Pets Welcome books / sites were ok but limited I found.
Looking at it from some of the property owners point of view - you have to remember a large proportion of animal lovers can be a little over defensive sometimes of their doggies - training is everything and I've met owners who love their dogs to bits but couldn't and shouldn't trust it in a cottage, B&B, or hotel. I train all my dogs to a standard where I can stay anywhere with them with confidence. The odd cottage owner has made a surprise visit which I suspected sometimes was to check out who was renting and what the dog was up to and I don't blame them. Plus if you stay in a guest house, hotel or pub you have to be aware of other people staying there who might not be dog lovers or might have phobias.
My doggie is a rescue dog by the way and was quite wild when we got her but now she has her own fan club around the country she is that friendly and well travelled.