CalMac had hoped that building work at the former linkspan berth would be far enough advanced to allow both its Wemyss Bay ferries to berth overnight at Rothesay - and had temporary Yokohama fenders delivered on Tuesday to allow this to happen.

But after trials were carried out using MV Argyle on Thursday, the vessel's captain, Linda Ward, decided the berth was not yet safe for the ferry to use - thwarting hopes of a return to a normal timetable in time for at least part of the Isle of Bute Jazz Festival weekend.

CalMac's regional manager for Bute, Brian Fulton, told us the trials had revealed a serious risk of the ferry 'chafing' against two of the main piles which have been sunk along the front of the pier.

"The fenders aren't attached to these main piles," he told The Buteman, "and there is a danger in the event of a high spring tide of the fenders riding up on to the pier.

"That would mean there would be nothing to protect the ferries, and that's a risk we weren't prepared to take.

"There was also a concern about the position of the overnight gangway for members of the crew.

"I'm very, very disappointed - I was very hopeful that the work would be sufficiently complete to allow us to get the service back some time this weekend, but it wasn't to be."

Mr Fulton warned that the building work at the pier may now affect the operation of the late night summer Saturday sailings, which begin on May 31 and offer additional sailings on Saturday nights at 9.10pm from Rothesay and 10pm from Wemyss Bay.

Since January 14, building work to reinstate the former side-loading linkspan berth has forced one of the two Rothesay ferries to berth overnight in Gourock, with the loss of one evening crossing from Wemyss Bay every day as a result.

The work has also caused the enforced cancellation of the last timetabled sailings from both Rothesay and Wemyss Bay on Friday nights only, because of the impact a diversion would have on crew members' working hours.