West Midlands Police is set to lead a massive regional force taking in the shire counties and five million people.

The plans have been revealed in a letter from Paul West, Chief Constable of West Mercia Police.

The Home Office has ordered police forces to come up with merger proposals after a review found smaller constabularies were unable to deal with organised crime and the threat of terrorism adequately.

Every force with 4,000 officers or fewer has been ordered to reform.

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This includes Staffordshire, West Mercia and Warwickshire Police. One option would be for smaller forces simply to merge with each other.

However, Chief Constables in the West Midlands region are to recommend the creation of one "regional" force taking in Herefordshire, Worcestershire, Shropshire, Staffordshire and Warwickshire as well as Birmingham and the Black Country.

It would employ 13,800 police officers and 20,000 staff.

The plans will be formally revealed on Friday.

But in the letter, sent to colleagues, Mr West said: "The most realistic options available to the force are to amalgamate with one or more other forces, or become part of a larger regional, strategic force.

"At the present time, the latter choice is emerging as the preferred option of other forces in the West Midlands region." Mr West hints in the letter that he is unhappy with the proposals.

He points out that West Mercia is already "performing extremely well".

The proposals were criticised by Meriden MP Caroline Spelman. She said: "This is being rushed, and we will have a shotgun marriage.

"The underlying problem is that the rural areas will lose out to urban areas."

Peter Luff ( Con Mid Worcestershire) said: "My strong view is that West Mercia Constabulary, which serves my constituents, is an extremely well run and effective force that needs to be allowed to get on with things.

"It would be quite extraordinary to say we need a regional police force, but that seems to be the way the Government is pushing us."

Referring to inner-city violence in Birmingham, he said: "We have seen only this weekend in stark terms how different the policing needs are in Birmingham and rural Worcestershire."

In a statement, West Mercia Police said a force covering the entire region was just one of the options under active consideration.

Paul Deneen, Chair of West Mercia Police Authority, said: "Figures to be published later this month will clearly demonstrate that the force is

achieving excellent results.

"As a Police Authority we share the force's recognition that there are areas that can be improved further but we must ensure that any replacement service is still locally accountable to the people it serves."

A spokesman for West Midlands Police said: "We will be sending our recommendations to the Home Office on Friday."

Plans have already been announced to merge West Midland ambulance, fire and health authorities.

The changes are seen by critics as a move towards a new tier of government in England, based on nine administrative regions.