A letter from NTS confirmed that as well as considering the closure of heritage sites, the board has given serious consideration to a merger with the National Trust.

The union is also disappointed to learn from the Chief Executive Kate Mavor that during a recent meeting with Alex Salmond, the First Minister’s reaction to pleas for assistance was luke-warm.

Prospect National Secretary Alan Denney said: “While calling on NTS to do everything possible to secure the jobs of its staff, and therefore preserve Scotland’s leading conservation charity for the people of Scotland, it came as a bolt from the blue to discover that active consideration had been given to merging with the National Trust south of the border.

“Such a merger would leave NTS as the significantly junior partner. We were therefore pleased to hear Chief Executive Kate Mavor report that their English counterparts do not wish to enter into any formal dialogue while NTS is in financial difficulties.”

The current redundancy exercise is designed to help the NTS eliminate its deficit this year and put money back in reserves in 2010. But Prospect fears this could pave the way for a merger to ensure the charity’s future sustainability.

“It would be cruelly ironic in this Year of Homecoming if the lack of government support meant that the newly-acquired Robert Burns Birthplace Museum ended up as a subsidiary of the NT, run and managed from Swindon,” said Denney.

“The National Trust for Scotland’s council – the governing body – is due to meet this Friday, and as far as we know the issue of merger has not even been put on the agenda for discussion.

“We believe the council should be given an explanation from the board, and its Chairperson Shonaig Macpherson, to account for its failure over several years to bring the Trust’s finances under control: this is not just about the credit crunch.”

Repeated requests by Prospect for copies of the board papers have met with a blanket refusal from the NTS, despite the union’s right to scrutinise the charity’s business case for the cuts.

The union believes that the level of secrecy in refusing staff representatives among others – including the NTS governing council – sight of the documentation that could seal the fate of the charity is unacceptable in the age of freedom of information, particularly when the charity is funded by membership subscriptions, donations and public money.

“We believe the NTS should be required to adhere to the same level of openness that we expect of other organisations spending taxpayer pounds,” said Denney.

The £21m Robert Burns Birthplace Museum project is the most ambitious ever undertaken by NTS. At a time when the host organisation is on the brink of ruin, the charity has diverted vast amounts of staff time and financial resources into this project.