I'm on holiday in the UK (Scotland, that is) and I have been rather unimpressed by the cell phone coverage here. Since I'm roaming, I can see the coverage for various providers (Vodafone, T-Mobile, O2, Orange). From within buses and trains on the countryside, most of the time there is zero coverage for any provider. In villages and small towns, Vodafone/O2/Orange have 2G coverage (at crawling 1 kbyte/s-or-less speeds), but only if you are outdoors in the right street; indoors and just around the corner, the signal may drop to zero bars. T-mobile has 3G, but even in fewer places than the other ones (I suppose 3G has inherently a smaller range from the tower). And I won't talk about using a cell phone while walking on a trail in the mountains/hills/shore... Even while walking around in the center of Edinburgh, I regularly get zero bars.
The good thing about it is that in the trains, buses, and restaurants, the other people are not bothering me with their phone conversations. :-)
There's a website that collects coverage data through an Android app and publishes them online: Sensorly, which confirms that it's mostly 2G in Scotland. Regarding spatial coverage, it suffers a bit from undersampling, though.
Note: my experience is from an HTC Desire S phone in a silicone rubber casing; I noticed in the past that the silicon reduces the GPS sensitivity, but I never noticed a difference for 2G/3G signals.