Rail groups have called for investment in Scotland's "forgotten line" connecting the south-west to the central belt after finding that passengers have been driven away by irregular timetables and infrequent services.

A report published by sustainable transport lobby group Transform Scotland found that trains running between Stranraer, Ayr and Glasgow were poorly patronised, with an average of 21 passengers per train, and complained of neglect by transport authorities towards the line.

Timetables on the route are skewed by the need to connect to Northern Ireland ferry services docking at Stranraer, leaving passengers waiting for up to five hours for some trains, the report found.

The planned move of Stena Line ferries away from Stranraer harbour to a port further up Loch Ryan is also likely to cut rail passenger numbers.

But the report's author, David Spaven, claimed there were "enormous opportunities" to attract more tourists onto trains. He said: "There is a significant potential day-trip market from Glasgow and across the Central Belt that could be tapped into should a satisfactory timetable be put in place."

The Transform Scotland study has been funded by Passenger Focus, the rail watchdog, and regional transport partnerships in Strathclyde and the south west.

A spokesman for Transport Scotland said: "We are currently working with Network Rail and ScotRail to explore how best to both meet the needs of the local community and drive up potential leisure passenger numbers to and from Stranraer."