There are three types of UK licence that can be taken one at a time to allow easy progression.

Foundation
The entry level is the Foundation Licence which is designed to get you involved in amateur radio as quickly as possible. It enables you to operate commercial equipment at low powers (10 watts) which is sufficient to contact other stations overseas.
(6 evenings study, includes practical assessments which are part of the exam.)

Intermediate
The Intermediate Licence allows you to operate at powers up to 50 watts, and build or modify your own equipment if you want. Part of the course is project based to give training in soldering and instrumentation.
(11 evenings study, includes project assessments which are part of the exam.)

Advance
This licence is for those who want to really get to grips with the theory and practice of radio communication and allows you the full permitted power on all bands. It is equivalent to the original RAE City & Guilds Examination before it was split up into the present three stages.
(15 evenings study, can be reduced by studying at home.)