Scotland's ferry network is facing major problems over the next five years as ministers grapple with the enormous capital cost of replacing ageing vessels while trying to work within a stringent budget.

Paul Finch, associate director of one the UK's leading transport consultancies, claimed the Scottish Government would have to find £240m to replace vessels which are nearing the end of their life cycle.

He warned that ministers would face "difficult decisions" about whether to reduce vital services to Scotland's islands in the forthcoming ferries review unless a way was found to fund replacement programmes.

Mr Finch, who has studied ferry routes for the Scottish Government and state-owned ferry operator CalMac, told The Herald that routes serving smaller island communities would be particularly vulnerable without a major funding commitment.

He said: "If you look at the age of the Scottish ferry fleet, there is serious investment required."

Mr Finch said the straitened economic circumstances facing ministers could lead to disappointment in the ferries review, which island communities have looked toward to improve links that are vital in sustaining them and halting population decline.

The analysis drew a frosty response from islanders yesterday and was rejected by the Scottish Government, whose spokesman said: "The Scottish Government is investing substantially to support and enhance lifeline ferry services to remote and island communities across Scotland, amounting to some £104m in the current financial year.

"We are presently investing £24.5m in a new vessel for Islay, and we are currently undertaking a comprehensive review of all Scotland's ferry services to look at what further positive changes and improvements can be made."