There's loads to choose from on the DLS, it depends which version of Trainz you have.....Top UK route creators are harcourt, gamerouche, angelah, puffernutter, hooverman, eso....
The oldest layouts ( UTC/TRS2004 ) may need some upgrading, but, you can choose from ECML South and Central which you can merge together to get the ECML from London Kings X up to Doncaster. Angela created a superb London Paddington to Reading for the WCL, there's also Paddington to Bristol in 8 separate sections which need scenery and trees adding to, which could be fun putting together....You can also look at Along UTA Lines, which harcourt built, it's a superb layout from Belfast to all the towns and cities in Northern Ireland. There's also a few routes set in Scotland, Glasgow to Oban and Fort William / Kyle of Lochalsh and Inverness to Aviemore, all of them are thoroughly recommended, by ME....:hehe:
If you have TS2009, Communist built a superb British layout, find his thread on this forum in the TS2009 section, it's worth downloading also.
Cheerz. ex-railwayman.