I've found Orange to be good in Scotland, The Lake District and where I live in the Yorkshire Dales. Indeed only Orange works here. They are also linked to T Mobile now so extra coverage in marginal areas. You should be able to get an Orange sim on a Dolphin, no contract plan where your only commitment will be to top up by £10 a month to get free internet and 400 free texts, You can probably wangle a magic number out of them too if you persist - 25p for upto 1 hour.
I definitely don't have any connection to Orange btw except that I have no choice but to use their services
"Never have a stupid argument with an idiot - he gets a lot more practice than you"
there I go again
not too hard really