England - Midlands
From the Warwickshire Avon in the south, to the Trent in the north

England - Northeast
North of the Trent drainage, flowing to the North Sea

England - Northwest
North of the Severn drainage, west of the Pennines

England - Southeast
Hampshire Avon drainage and eastwards, with the Nene as the northern limit

England - Southwest
The Somerset Frome and Dorset Stour and westwards

Scotland - Central Highlands
Rivers 'near' Perth

Scotland - Far North
Rivers 'near' Inverness

Scotland - Northeast
Rivers 'near' Aberdeen

Scotland - Southern Uplands
Rivers south of Glasgow

Scotland - West Highlands
Rivers 'near' Fort William

Wales - North
Severn/ Rheidol catchment and north

Wales - South
South of Severn/ Rheidol catchment

Everywhere else
Rest of the world