A few more observations about coverage and speed.
At home, central Newcastle, I am impressed with Three. I always get in excess of 2Mbps, often 2.5Mbps. However, in Newcastle I rarely need it. Being a BT Total Broadband customer I get free access to BT Openzone, which is pretty much ubiquitous in the city, and generally faster.
On the train journey to London, one I have to do nearly every week, coverage on Three is almost continuous, with speeds around 1Mbps. Compared to O2, this is excellent. This alone is worth a tenner a month to me.
But once you get to London, it's a totally different story. Here, even high up in my hotel near Kings Cross, and with a full five bars of signal, I am struggling to get 120Kbps, which is very disappointing. I can only assume the issue here is one of contention?
So, a mixed story. Generally good, and good value, but those who spend most of their time in London (poor sods) may be better off with one of the other networks.