Forecasts for Scotland's nascent marine energy industry are "wildly overoptimistic", and much of the public money invested has been poor value, according to a leading economist.

He also says Alex Salmond's description of Scotland as the "Saudi Arabia of marine energy" may well come back to haunt him.

Tony MacKay, of Inverness-based Mackay Consulants comments on the industry in the North East Scotland Economic Monthly Report.

He says: "December was a bad month for Scotland's fledgling marine energy industry, with problems at two of the leading companies. Pelamis Wave Power closed down, with the loss of another 16 jobs bringing the total to 56, and Aquamarine Power laid off more than 30 of their staff. "

He says the Scottish Government's main reaction was to set up another quango, but he is sceptical it would do any better than "the plethora of existing public bodies involved."

He had been a strong supporter of the marine energy sector but had tried to take a realistic approach to its prospects.

"That has been in marked contrast with the wildly overoptimistic forecasts of the Scottish Government, Highlands and Islands Enterprise (HIE) and Scottish Renewables, the industry's representative body. "

He takes issue with the Scottish Government forecast that the marine energy industry could be worth £6.1 billion by 2035, creating nearly 20,000 jobs.

He says there is a strong consensus in the industry that some tidal projects are close to becoming commercially viable, but that wave energy has made "very disappointing progress. "

"There are very good economists in both the Scottish Government and Scottish Enterprise, so I do not understand how they have allowed such a waste of public money on wave energy projects. "

He contrasts industry body Scottish Renewables with "some excellent" representative bodies in Scotland, such as Homes for Scotland and the Scotch Whisky Association .

"I have had a few professional disagreements with Oil & Gas UK over the years but they have done a very good job for their industry. Unfortunately, Scottish Renewables do not fall into that category. They seem to believe that their main function is PR and that they must attack anybody like myself who tries to present realistic opinions on the renewable energy industry in Scotland. "

But Lindsay Leask, Senior Policy Manager at Scottish Renewables, said the organisation was the voice of more than 300 companies in an industry employing over 11,000 people and one which was now Scotland's largest single source of electricity.

But she said the sector had faced a number of challenges in recent months.

The Scottish Government's belief in the future success of marine energy is undiminished., a spokesman said.

"Now is the right time to consider the future of our support for wave energy in Scotland. This is a young industry and we still have a lot of learning to do in marine renewables.

"We want to encourage further innovation in wave energy development and we recognise the need for a bold new approach to supporting this emerging technology. There is also a lack of design convergence in wave energy with many different concepts in development, while tidal appears to be converging on a front-runner design."

He said this meant that while the tidal energy sector was ready to build array demonstration project, such as the MeyGen project in the Pentland Firth, the wave energy sector had to evolve further to gain the confidence of investors.

A HIE spokeswoman said: "Wave Energy Scotland will play a key role in helping developers in Scotland overcome the present difficulties which are affecting the sector worldwide, and make that vision a reality."