I have found Vodafone's signal way, way better than any other network (and yes, I've used them all)....Vodafone don't necessarily have the biggest 3g network, so you might not get fast internet everywhere, but their network is WAY more reliable than any of the others, and if you have a signal you've got no chance of it going unless you really are on the border (unlike 3 and o2).
The best thing about Vodafone is that if you do have signal problems at home, you can get hold of Vodafone Sure Signal. Provided you have a wired internet connection you can use this as essentially your own little mast. You might want to check whether your internet at Lancaster lets you use more than one device, and/or wired devices at all, before you buy one though. It's a genius product is Sure Signal, and something none of the other networks are able to provide in any realistic capacity...