After a renaissance in new light rail systems in the 1990's, light rail expansion in new cities has dramatically slowed. However, the isles still have a healthy share of trams, light rail and a few metros. The newest to open will be Edinburgh's scandal filled light rail line.
We also pay honourable mention to the Channel Islands' 3 km Alderney Railway, which uses London tube cars hauled by a diesel engine.
One final note: If you see the word "subway" in Great Britain, don't be fooled. The phrase refers to what we Americans call an underpass. It is simply an underground passageway used by pedestrians.
Other Links of Interest
Are Back On English Streets