West Mercia Police looks certain to be merged with a neighbouring force after a major report found that it was too small to meet the demands of the 21st Century.

A policing review by HM Inspector of Constabulary Denis O'Connor recommended a standard police force size of about 4,000 officers.

West Mercia, which has 2,422 officers, now looks unlikely to escape a forthcoming shake-up of the constabulary system based on the report's findings.

There are three neighbouring forces which could be merged with West Mercia to meet Mr O'Connor's target force strength.

Warwickshire has 1,012 officers, Gloucestershire has 1,308 and Staffordshire has 2,309.

West Midlands police, with 8,154 officers, is not expected to be enlarged any further.

The Home Secretary, Charles Clarke, is understood to support the HMIC's plans and has invited police chiefs to London on Monday to discuss them.

A public announcement is expected later in the day, although the Home Office said there would be no details relating to mergers between specific forces.

A West Mercia spokeswoman said it had no comment to make at the moment.

Chief Constable of West Mercia, Paul West, and chairman of West Mercia Police Authority, Paul Deneen, are going to meet Charles Clarke on Monday and we will know more then," she said.

However, Mr O'Connor's report gives little hope for West Mercia to continue in its current form.

He wrote: "The findings are stark - very few forces assessed fully meet the required standards.

"It is also apparent that size matters - larger forces are likely to have a much greater capability and resilience whilst smaller forces in many cases find it harder to provide the services to an acceptable standard."

Mr O'Connor accepted the difference in standards between large and small forces was not uniform.

But there remained a clear trend that smaller forces did not have the specialist capacity to deal with major terrorist incidents or serious organised crime.

He added: "Forces with over 4,000 officers or 6,000 staff tended to meet the standard across the seven proactive services measured in that they demonstrated good reactive capability with a clear measure in proactive capacity.

"Forces below that size tended to fall some way short of the standard with in general the smallest forces faring the least well."

Mid-Worcestershire MP Peter Luff said he would take a lot of persuading before he supported changes to the police force.

He said: "In West Mercia we have a police force fit for the purpose. The kind of crime we have in West Mercia is most appropriately policed by a force of the size we have got.

"I would like to see more officers, but I don't want to see structural change. That would distract the police in their work of fighting crime."