SNP ministers pumped hundreds of thousands of pounds into a flagship marine energy prize that collapsed because no one could win it.

The Scottish Government revealed it had spent almost £400,000 sustaining the doomed Saltire Prize over the past six years despite a lack of applicants and impossible criteria for victory.

However the true costs may be closer to £800,000, as the government said it only had payment records dating back to 2012, and the prize was launched in 2008.

Most of the money went into “resourcing costs” for the expert judging committee.

When then First Minister Alex Salmond announced the £10m prize he hailed it as “one of the biggest international innovation prizes in history”.

He said: “The Saltire Prize has the potential to unlock Scotland’s vast marine energy wealth, putting our nation at the very forefront of the battle against climate change, to make a lasting and decisive difference to our planet”.

However the prize sank beneath the waves because the technology wasn’t up to the task.

Contenders had to show they could generate commercial electrical output from wave or tidal power for at least two years in Scottish waters.

The prize period was initially set at seven years, then extended by another two years.

By 2013, five firms were in the running, but it was clear the hopefuls were struggling.

A year later, one of the five, the wave power firm Pelamis went into administration, followed a year later by Aquamarine Power.

When the deadline passed in June 2017 without a winner, the government admitted “the path to commercialisation [was] proving more difficult than initially anticipated”.

In February, Nicola Sturgeon said she had asked officials to “reshape the prize” and had commissioned research on the state of the industry which would be published “shortly”. It has yet to appear.

It later emerged the committee overseeing the prize had concluded as early in 2014 that the prize could be not won within the timescale set down.

The new cost data, released under freedom of information, shows “committee resourcing costs” of £62,000 in 2012/13 and £100,000 in 2013/14 before a sharp drop off in their bills.

Other significant expenditure included £68,000 on “saltire prize rebranding/secondment costs” and almost £6000 on developing a Saltire Prize website in 2012/13.

A “Saltire Prize grand challenge launch” in 2012 cost £1660, while £1910 went on two dinners for the judging committee in 2012 and 2013 at a renewable energy conference.

There was also a large amount of spending on projects to reinforce the Saltire Prize brand.

They included almost £50,000 sponsoring a PhD between 2014 and 2016, £60,000 on a “Junior Saltire Prize” for school pupils between 2012 and 2016, and £1800 in 2015 sponsoring a “Saltire Prize lecture”.

However the costs also reveal the difficulties behind the scenes, with £3760 spent in April 2014 of a “Saltire Prize redesign study” and £27,744 in March this year on commissioning the “state of the industry report” which the First Minister referred to the previous month.

Hosting the Saltire Prize website is still costing taxpayers £500 a year.

Total costs associated with the Saltire Prize from 2012/13 to 2017/18 were put at £393,546.

LibDem MSP Liam McArthur, who has asked Ms Sturgeon about the prize at Holyrood, said: “It’s been clear for quite some time that, as it stands, the Saltire prize is dead in the water.

“Ministers can’t kid themselves or the public that ‘steady as she goes’ is a credible strategy.

“This prize money was supposed to spark innovation and put Scottish marine renewables on the global map.

“As things stand, all Ministers are likely to achieve is growing industry-wide frustration.”

A Scottish Government spokesperson said: "We are determined to provide a supportive environment for the successful development of marine energy and the industry has taken important steps forward since the Saltire Prize was established in 2008.

"The prize has helped draw international attention to the potential of marine energy, sparked the interest of technology developers around the globe, and put Scotland’s world leading marine expertise on the map."