Labour politicians claim a three year trial of a new ferry service is a sham because it is running only in the winter when half the sailings are cancelled.

The ferry from Oban to South Uist normally takes over five hours and nearly seven if it has to go to Barra first. So most islanders on South Uist believe a three-and-a-half hour service to Mallaig is the answer.

But Highlands and Islands Labour MSPs, Rhoda Grant and David Stewart, together with Labour's Prospective Candidate for the Western Isles Alasdair Morrison, have cast doubts on the three year pilot of the Lochboisdale-Mallaig route.

Mrs Grant tabled Parliamentary Questions asking how many times the service had been cancelled since the trial began in November 2013, if there were plans to extend the trial to run during summer months and how much it would cost to run a year round service.

She said that figures that were returned showed a 49% cancellation rate during the first year of the trial with the figure increasing to 60% in the first two months of the second year.

Mrs Grant said "It has become very clear that it is impossible to accurately evaluate the worth of the pilot, given the number of cancellations that have been experienced. People can't depend on the service running and it will therefore be underused."

Labour's Prospective Candidate in the Western Isles, former Scottish Executive minister Alasdair Morrison, said "The so called pilot on Lochboisdale-Mallaig route is an insult to the communities of South Uist. Clearly, the pilot was set up with a view that it would fail. "

But Transport Scotland spokesman said a summer pilot service was not currently possible due to "vessel deployment limitations."

He said it was unfortunate that the severe weather over the winter months had affected the operational running of many services to the Western Isles, including the Mallaig-Lochboisdale pilot service.

"The pilot service will however be evaluated over the full three year pilot period. Before decisions are made about the future the pilot will be assessed against agreed success criteria, which will take into account the severe weather disruptions experienced and the winter-only nature of the pilot. "