I think the regions are divided up into counties as follows:
East Midlands: Derby, Derbyshire, Leicester, Leicestershire, Lincolnshire, North East Lincolnshire, North Lincolnshire, Northamptonshire, Nottingham, Nottinghamshire, Rutland
Eastern England: Bedford, Cambridgeshire, Central Bedfordshire, Essex, Hertfordshire, Luton, Norfolk, Peterborough, Southend-on-Sea, Suffolk, Thurrock
London: Greater London
North Wales: Clwyd, Gwynedd
Northeast England: County Durham, Darlington, Hartlepool, Middlesbrough, Northumberland, Redcar and Cleveland, Stockton-on-Tees, Tyne and Wear
Northern Scotland: Central, Fife, Grampian, Highland, Orkney Islands, Shetland, Tayside, Western Isles
Northwest England: Blackburn with Darwen, Blackpool, Cheshire East, Cheshire West and Chester, Cumbria, Greater Manchester, Halton, Lancashire, Merseyside, Warrington
South East England: Brighton and Hove, East Sussex, Kent, Medway, Surrey, West Sussex
South Wales: Dyfed, Gwent, Mid Glamorgan, Powys, South Glamorgan, West Glamorgan
South West England: Bath & North East Somerset, City of Bristol, Cornwall, Devon, Isles of Scilly, North Somerset, Plymouth, Somerset, South Gloucestershire, Torbay
Southern England: Berkshire, Bournemouth, Buckinghamshire, Dorset, Gloucestershire, Hampshire, Isle of Wight, Milton Keynes, Oxfordshire, Poole, Portsmouth, Southampton, Swindon, Wiltshire
Southern Scotland: Dumfries and Galloway, Lothian, Scottish Borders, Strathclyde
West Midlands: Herefordshire, Shropshire, Staffordshire, Stoke-on-Trent, Telford and Wrekin, Warwickshire, West Midlands, Worcestershire
Yorkshire: East Riding of Yorkshire, Kingston upon Hull, North Yorkshire, South Yorkshire, West Yorkshire, York
Corrections welcome!