Shetland MSP Tavish Scott has accused ministers of forcing his constituents to subsidise the Western Isles through preferential treatment on ferry fares.

While the Orkney and Shetland services, and those to Argyll and Bute, face fare increases of inflation plus 0.5%, services to the Western Isles are part of a pilot scheme looking at Road Equivalent Tariffs and have been frozen until 2010.

The Liberal Democrat leader said: "SNP Ministers presumably hope that their special treatment of the Western Isles will help them to hang onto their parliamentary seats there. But those on Scotland's other islands will not forget this when they pay above inflation fare increases next year nor when they vote."

But a Scottish Government spokeswoman called Mr Scott's claims inaccurate, saying: "In the most recent contract year, the Scottish Government provided increased financial support of some £29m to NorthLink Ferries to operate the services. This is already some 57% of the cost of providing the services.

"The cost of fuel has increased significantly and the Scottish Government has largely absorbed these costs with only a marginal increase of fares for users."

She added: "We are also currently piloting a Road Equivalent Tariff (RET) approach to setting fares in Scotland as we believe that is a good way to deliver cheaper fares for islanders, tourists and businesses.

"While initially focusing a pilot on the Western Isles, we want this test case to pave the way for cheaper fares for all our island communities."