The paddle-steamer Waverley embarked on its summer season yesterday, taking 700 pensioners down the Clyde, but delays to renovation work on Largs pier have put a fresh cloud over the vessel's future.

Iain MacLeod, of the vessel's owners, the Waverley Steam Navigation Company, has written to his MSP asking him to press for government action to speed up work at the Ayrshire resort.

In his letter to David Whitton, Labour MSP for Strathkelvin and Bearsden, Mr MacLeod says the future of the vessel, which has received around £5m of public investment in recent years, could be at stake.

"The viability of Waverley's crucial Scottish season and indeed her entire future is seriously threatened by the failure of CMAL, the Scottish Government's maritime infrastructure company, to make arrangements for her to call at Largs Pier," he wrote.

"The pier is under reconstruction and the project has been delayed. The original timing of the work was planned so as not to interfere with Waverley but in the face of the delay CMAL has so far been unwilling to make arrangements for passengers to have access.

"After a difficult season in 2008 when the weather played havoc with plans, Waverley's 40,000 regular supporters, very many of them Scottish, have raised £250,000 to ensure she can sail in 2009 and keep alive the tradition she alone preserves.

"Waverley means a great deal to the Scottish people. Now her entire future is threatened. The 11,500 passengers who join her at Largs in a typical season are the difference between a successful season and a loss-making one. Waverley could not survive another loss-making season."

Mr Whitton said: "The Waverley is one of our most cherished institutions and I have already raised it with the Transport Minister.

"I am deeply concerned that the Waverley's summer season is now threatened because construction work on Largs Pier has over run. The Scottish Government needs to step in and knock heads together to find a solution."

Scottish Conservative leader Annabel Goldie has also got involved, saying: "I have written to the minister to raise concerns regarding the delayed work on Largs Pier.

"I know that the Waverley's passengers, many from Largs and wider North Ayrshire, are very keen to get aboard and enjoy the journey and they too wish the pier finished quickly, so that they are able to do just that."

Kathleen O'Neill, general manager at Waverley Excursions, who operate the paddle-steamer, said: "CMAL have said they could advance the programme by eleven days but say they don't have the funds to do so."

But a spokeswoman for CMAL denied money was the issue, saying that purely technical reasons meant they could only give safe public access from July 24, while work continues beyond that.

"The three-week delay was caused by the discovery of Victorian piling. We have given a lot of time and consideration to getting this work done more quickly but it has just not been technically possible," she said.

A Scottish Government spokesperson said: "CMAL are the owners of Largs pier and responsible for all related operational matters. CMAL and Waverley Excursions have discussed a number of options to minimise any disruption to the Waverley schedule during the works at Largs pier, including accommodating the Waverley at Wemyss Bay."

The renovation of the pier, which dates from 1845, is costing £6m. Waverley, which is registered to carry 925 passengers, was built in 1946 as a replacement for an earlier Waverley that was sunk in 1940 helping with the evacuation of troops from Dunkirk.

The new 693-tonne steamer was launched in October 1946 at builders A & J Inglis, Glasgow, and entered service in June 1947. She was built for the London & North Eastern Railway Company to sail on their Firth of Clyde steamer fleet.

She is the last sea-going paddle steamer left in the world. Her restoration and rebuild was completed in 2003, at a cost of £7m. She has an Art Deco restaurant, bar for 200 people and a tea room. The famous steam engines are open for the passengers to view. However, she has also been involved in several scrapes, most notably as she approached Dunoon in July 1977. The vessel was left aground and extensively damaged after striking rocks.