Networks

As more and more people use mobile phones, the networks are building more bases, and coverage improves all the time. Most of the time, all the networks' coverage is easily good enough for most people.

Orange has had a policy of installing many more base stations than its rivals, and uses GSM 1800. The solidity of coverage seems excellent.
Network Coverage Map >

Vodafone has always been the leader in terms of UK subscribers, and has consistently been in the lead in terms of coverage with mostly 900MHz bases.
Network Coverage Map >

O2 mostly uses GSM 900 but also uses 1800MHz frequencies to increase capacity. Their map shows planned maintenance and GPRS coverage.
Network Coverage Map >

T-Mobile is a GSM 1800 network. They are now catching up with their competitors, but their coverage area is not quite as wide as that of the others.
Network Coverage Map >