An expert has successfully challenged ministers' claims that they are prevented from giving islanders publicly owned land for nothing because of a piece of Tory legislation.

Now the Scottish Government has conceded its own internal financial regulations are likely, although not certain, to be the obstacle.

The 1100 residents of Barra and Vatersay are considering a community buyout of local land, but there is a debate as to how much would actually have to be bought.

In 2003, the late clan chief, Ian Macneil of Barra, announced he had agreed to donate his crofting estate on the island to the then Scottish Executive.

However, he made clear that if islanders wanted the 9000 acres, they were to be given the estate free of charge at a later date.

The islanders also have in their sights more than 7000 acres already owned by the Government. In total, there are 16,000 acres, with more than 440 croft tenancies and two working quarries.

When the Macneil transfer was completed in 2004, the then rural affairs minister Ross Finnie said: "We intend to manage this land with a view to its transfer, along with our own properties, to community ownership at a time appropriate to the islanders of Barra."

The ambiguity of the statement raised local hopes there might be no charge, but a Scottish Government spokesman said: "The Transfer of Crofting Estates Act sets out that any Government-owned land sold would be subject to the independent valuation applied by the District Valuer."

The legislation was introduced in 1997 by the then Scottish secretary, Michael Forsyth.

But it has only been used once, in 2010, when the West Harris Trust completed its £59,000 purchase of 52 crofts and more than 16,000 acres on the three Government-owned crofting estates of Scaristavore, Borve and Luskentyre.

However, acclaimed Highland historian Professor Jim Hunter – who wrote a book on community ownership of land in the Highlands and Islands, published last year – told The Herald: " It's not the case that the Transfer of Crofting Estates Act stipulates a purchase price based on valuation.

"What the act actually says, in Section 1(4) is: 'The disposal of property under this act shall be on such terms as the secretary of state, with the consent of the Treasury, may agree with the body acquiring the property'."

He added the Scottish Government now took the place of the secretary of state.

But it had been clear during the passage of the 1997 act that the then Tory government foresaw circumstances where land should be passed over for nothing.

He claimed that in 1996 – when introducing the legislation in the House of Lords, where it started its parliamentary journey – Lord Lindsay, then a Scottish Office minister had said: "There is a need for flexibility to strike the right balance in individual cases between the interests of the local crofters and those of the taxpayer.

"Each application will be looked at on its merits but my right honourable friend [Michael Forsyth] has made it clear the Government is prepared to consider transfer at no consideration, where this is necessary, to make sure the trust (community or crofting) gets off to a good start."

Following Mr Hunter's challenge, the Scottish Government clarified its position in a statement.

Referring to the 7000 acres which were not part of the Macneil legacy, the Government statement said: "The Scottish Public Finance Manual requires best value to be achieved for any land in the Scottish Ministers' estate and therefore the rest of the land is likely to be subject to independent valuation applied by the District Valuer."

Islanders have already called for the issue to be cleared up.

Eoin MacNeil, development manager for Voluntary Action Barra and Vatersay, said: "We need clarity at an early stage on what we will be faced with if we decide to go down the road of a community buyout and how much we might need to raise."