B&B's tend to be in places people want to go, so anywhere with tourists will have them, but places without tourists tend not to, but they can be found. Not all are listed in books or on websites and the standard (and costs) can vary enormously, from something equivalent to a 3 star hotel to something not as good as a youth Hostel
A lot of pubs offer B&B as well, but as they may only have one or two rooms dont make a big issues of it.
Wild Camping: Is certainly possible in the UK, but you tend to be talking about woods and moorland
Stealth Camping: Iis also possible, you need to be discreet, and careful of where you camp, but I've camped in some amazing places, such as the garden of the health clinic, overlooking the Thames, we just had to be gone before they opened in the morning.
Fly-Camping: When you just ask around before resorting to Stealth or Wild, the best places to ask are the local pub, I've spend many a night camping in a pub garden, and a few more on local fields and other gardens for people in the pub.
Youth Hostels are worth looking at
Cheap hotels: There are a few chains, all mentioned by others above, they are not particularly cheap, nor particularly good. A B&B would typically offer a better place for a better price (Which is probably why in the UK we have a relatively few chain hotels when compared to the USA)
Camp Sites: In the UK,like B&B's they vary enoumously in price and quality and tend to be found in the same sorts of paces, wherever tourists stop.
In places like France they have a much better 'Camping Municipal' system.
.
