As I see it:
Champions League: West Highland Line Helensburgh-Oban/Fort William, Kyle Line
Premier League: WCML Lancaster-Glasgow, Settle Carlisle, Highland Mainline, Far North Line, Cumbrian Coast, ECML North of Morpeth to Aberdeen, Whitby Branch, GWML Exeter-Penzance, St Ives Branch, Kilmarnock-Carlisle
Championship: Bentham Line, The Marches, North Wales Coast, Aberdeen-Inverness, Tyne Valley, Huddersfield-Stalybridge, Hope Valley, Ayr-Stranraer, Scarborough-Hull, Chiltern Mainline, WCML South of Lancaster, Heart of Wales, Lowestoft-Ipswich, Durham Coast, ECML York-Morpeth, Newton Abbot-Paignton
I'm yet to travel the Cambrian, or the Marston Vale...