Some areas are relatively simple, but there is a large part of England where there are no obvious natural subdivisions and for historical ones you have to go back to the seven Anglo-Saxon kingdoms of the Heptarchy, before the tenth century.

The problems can be seen in the attempts by Wessex regionalists to define a Wessex region they can all agree on. Between the shifting boundaries of the historic Kingdom of Wessex, the Wessex of Thomas Hardy and the attempts of Cornwall and some in Devon to assert a non Wessex celtic heritage; the south west and south central portions of the map are problematic.

http://en.wikipedia.org/wiki/Wessex

Region (including)

1. Berks, Bucks and Oxon or possibly North East Wessex (Berkshire, Buckinghamshire, Milton Keynes, Oxfordshire).

2. Cornwall (Cornwall, Isles of Scilly). It might possibly link with Devon, but Cornwall is the most distinctive English county, with its own celtic heritage.

3. East Anglia  (Cambridgeshire, Norfolk, Peterborough, Suffolk). A Kingdom of the Heptarchy.

4. Essex  (Essex, Southend on Sea, Thurrock). One of the Kingdoms of the Heptarchy and a large modern shire county.

5. Greater London (Greater London). The one region which is already a reality.

6. Hampshire (Bournemouth (could go with its post 1974 county of Dorset or its pre 1974 county), Hampshire, Portsmouth,  Southampton). A part of the historic Kingdom of Wessex, Winchester was Alfred the Great's capital. However it is one of the larger shire counties, which I would see as distinct from the south west. The Isle of Wight might be included but I suspect the Islanders would strongly prefer their own small region.

7. Isle of Wight (Isle of Wight).

8. Lincolnshire (Lincolnshire, North Lincolnshire, North East Lincolnshire). It could possibly link with the Midlands or East Anglia, but it is a historic county which does not quite fit with anywhere else.

9. North East England (Darlington, Durham, Hartlepool, Northumberland, Stockton on Tees, Tyne and Wear). This is more or less the existing region. It rejected an elected regional assembly at a referendum, but a body with worthwhile powers might be more acceptable.

10. North Mercia (Derby, Derbyshire, Leicester, Leicestershire, Nottingham, Nottinghamshire, Rutland, Staffordshire, Stoke-on-Trent).

11. North West England (Blackburn with Darwen, Blackpool, Cheshire, Cumbria, Greater Manchester, Halton, Lancashire, Merseyside). This is the existing region. Possibly Cumbria might see itself as distinct enough to want to be a small region.

12. South East England (Brighton and Hove, East Sussex, Kent, Medway, Surrey, West Sussex). This is a fairly cohesive geographical area with some historical ties. It combines two of the smaller Heptarchy kingdoms (Kent and Sussex) with the territory between them and the Thames (Surrey).

13. South Mercia (Bedfordshire, Hertfordshire, Luton, Northamptonshire).

14. Wessex (Bath and North East Somerset, Bristol, Devon (unless it links with Cornwall), Dorset, Gloucestershire (possibly), North Somerset, Plymouth, Poole, Somerset, Swindon, South Gloucestershire, Torbay, Wiltshire). Not absolutely the same as the historic or literary Wessex, but you have to draw the boundaries somewhere.

15. West Mercia (Herefordshire, Shropshire, Telford and Wrekin,Warwickshire, Worcestershire). Counties around and to the west of West Midlands.

16. West Midlands (the metropolitan county of West Midlands, around Birmingham, not the larger current region). This is a large urban area. It could be treated separately from the rest of the Midlands.

17. Yorkshire (East Riding of Yorkshire, Hull, Middlesbrough*, Redcar and Cleveland*, South Yorkshire, North Yorkshire, West Yorkshire, York)