The Scottish Executive said more information was needed on the proposals by Scottish Natural Heritage (SNH).

Deputy Environment and Rural Development Minister Allan Wilson said he wanted to know more about the experiences of other countries which have introduced similar schemes.

I appreciate that a great deal of effort has been put into developing this proposal Allan Wilson Deputy Environment Minister

However, the Scottish Wildlife Trust (SWT) said it was "extremely disappointed" by the move.

Chief executive Steve Sankey said: "We... cannot explain why the minister feels that there's insufficient information for him to make a decision.

"After several favourable consultative rounds and years of deliberation over meeting international criteria we think the minister has bottled out of making a decision.

"The executive is selling Scottish wildlife short and is missing a superb opportunity to stimulate the economy of Argyll."

SNH sought permission to re-introduce the animal to the wild some 400 years after it disappeared.

Electronically tagged

The government agency proposed placing a dozen European beavers in Knapdale Forest, Argyll as an initial trial.

They would be electronically tagged and monitored as they move around Forestry Commission land.

SNH argued that beavers could help improve the habitat, supporting more fish and bird species.

SNH is grateful for the minister's response, although we are disappointed that we are not able to proceed with the scientific trial immediately SNH spokesman

A survey of people in the area suggested that 64% were in favour, 24% against and 12% did not express a clear opinion.

However, Mr Wilson has now written to SNH chairman John Markland to say that he needed more information before he could agree to the proposals.

He said further consideration of the potential risks to agricultural, forestry and salmon interests was needed.

There should also be a further look at the financing and management of the trial, as well as a thorough assessment of any public health risks.

Mr Wilson said: "I appreciate that a great deal of effort has been put into developing this proposal, and recognise that SNH have attempted to address the wide range of complex legal, ecological and economic issues required in such an application.

Longer-term impacts

"However, I am currently unable to grant approval for a licence under Section 16 (4) of the Wildlife and Countryside Act 1981 on the basis of the information as presented.

"It would be helpful to know more about the experiences of other countries where European beaver have been introduced, including any longer-term impacts."

SNH said it hoped to continue discussions with officials.

Pilot project

A spokesman said: "SNH is grateful for the minister's response, although we are disappointed that we are not able to proceed with the scientific trial immediately."

A pilot project is already up and running on marshland in Kent, England, where a family of beavers was introduced earlier this year.

Conservationists are considering an initiative to return the animals to the wild in parts of south West Wales during the next two years.