The Home Office wanted Wales' four police forces to merge

The South Wales and North Wales forces spent over �400,000 each. Dyfed-Powys Police spent �227,000, while figures for Gwent Police were not available.

South Wales Police Authority is the second in Wales to ask the Home Office to reimburse its costs.

The Home Office said it would meet some costs but not "sign blank cheques".

All four Welsh forces were critical of the plans, announced in the wake of the 7/7 London bombings, to create a single force in Wales.

This half a million pounds in the case of South Wales and North Wales will have to be found somewhere. Otherwise... there'll be talk of cuts Elfyn Llwyd MP

The UK Government said it wanted to reduce the number of forces in Wales and England from 43 to 24, claiming smaller forces were not able to deal effectively with the threat of international terrorism or organised crime.

In July this year, the Home Office announced that the idea of police mergers was being abandoned because of wrangling over funding.

Figures obtained by the BBC give a clearer picture of the cost. The total cost to all 43 forces is expected to be well over �6m.

'Timetable'

North Wales Police Authority has already said it is asking for �375,000 compensation from the Home Office to cover the costs of its research into the abandoned mergers plan.

Ray Thomas, chair of South Wales Police Authority, told BBC Wales the money had not been "totally wasted," but the authority would still ask the Home Office for money.

North Wales Police was the most critical of the merger plan

He said: "Certainly on the merger itself, we could have done better with the money.

"It's basically a job well done. We know the facts and figures throughout Wales now in relation to what we want to achieve and hopefully if we get some of the costs back it puts us in good stead for the future."

Elfyn Llwyd, Plaid Cymru MP for Meirionnydd Nant Conwy, a firm critic of the merger plan from the outset, said the police authorities were justified in asking for the money, having responded to the Home Office's "unrealistically short timetable".

He said: "Police authorities normally are existing from hand-to-mouth. They're not overpaid each year and inevitably, this half a million pounds in the case of south Wales and north Wales will have to be found somewhere within the budget.

"Otherwise what we're going to find in the next round of funding is they'll be strapped for cash again and there'll be talk of cuts."

The Home Office said: "If a police force diverted current staff towards the restructuring project then we wouldn't regard that as having incurred extra expenditure.

"Extra expenditure is only when they have employed new people, or resources, for the project. We will only reimburse forces where we feel it is reasonable."