Island politicians last night vowed to oppose any attempt to merge their local health boards with larger mainland authorities.

Some see the Scottish Government's decision to form partnership agreements between Orkney/Shetland and Grampian, and Western Isles and Highland, revealed in The Herald yesterday, as the first step to merger.

Others in the islands have accepted ministers' assurances that the initiative is designed only to provide managerial and administrative support for the island boards, and will not undermine their autonomy.

However, Tavish Scott, the LibDem MSP for Shetland, was not persuaded. He saw the partnership arrangement as just the start of a centralising process that posed a threat to the autonomy of island authorities.

He said: "I think the SNP has decided that small doesn't work and the logic of that is that island health boards will be eventually subsumed into larger mainland authorities. The greater logic is that we will lose our island authorities to a Strathclyde writ large.

"We are having none of that. It is deeply worrying. It is also typical of the SNP that there has been no announcement in parliament and the news of this comes during the two months when ministers cannot be held to account by parliament. So I will be writing today to the Health Minister, demanding to know what's going on."

He said that Shetland was having to pay a price for serious management failures revealed in the Western Isles health board. "Problems elsewhere should not produce a one-size-fits-all approach to all the island health boards."

The news also caused concern in the Western Isles. Angus Campbell, vice-convener of Western Isles Council, said the council had anticipated closer integration of its services with those of the health board, rather than the board strengthening ties with mainland health authorities.

"There is still residual fear in some quarters about the long-term future of island health authorities and this proposed development only creates further uncertainty. The long-term aims of both organisations (council and health board) are to have effective joint service provision within the islands to ensure the best use of resources and services and retain maximum employment within the area."

Stephen Hagan, convener of Orkney Islands Council, shared those concerns. "We have a solid relationship with NHS Orkney and have been engaging in constructive discussions on shared services. We hope that the proposed partnership arrangements will help to strengthen the board's management and enhance its independent status."

But island health boards had a different perspective. Sandra Laurenson, chief executive of the Shetland board, said: "We are supportive of the proposal in principle. We already work closely with Grampian on clinical services, so we can see the benefit of working together on support services. We are very pleased the independence of our board has been confirmed."

Orkney NHS also welcomed the proposal and did not see it as any threat to its own independence.

A statement from NHS Western Isles said Health Secretary Nicola Sturgeon had reaffirmed on her visit to Benbecula on Tuesday that the board would continue to exist independently. "The purpose of establishing stronger formal partnerships would be to strengthen the capacity in the Western Isles - not to dilute it."