Largest in height is Snowdonia in North Wales, the highest mountain, Snowdon, is 1085m above sea level.
If you're talking about length, its the Cambrian Mountains. They stretch for 65 miles north to...
Grampian Mountains, parts of which are the Cairngorms where 4 of Scotland's highest mountains can be found: Ben Macdhui, Cairntoul, Cairngorm and Braeriach, all over 4,000ft.