Upgrades to Scotland's rail network could boost plans to cut Glasgow to London journey times to just over three hours, a leading think tank has claimed.

The introduction of new high-speed lines would also see passengers spending less time travelling between key Scottish cities, according to Greengauge 21.

In a report outlining its vision for Britain's railways by 2040, the transport think tank also claimed high-speed rail connecting all of the UK mainland would put "rocket fuel" in the country's economy and significantly raise productivity.

Jim Steer, director of Greengauge 21, said: "To transform productivity across the whole of Britain, we need to transform connectivity for dozens of cities the length and breadth of the country.

"The plans for Scotland are particularly striking and will bring a radical improvement to rail connectivity both within Scotland and across the English border."

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The proposals include a new high-speed line in Lanarkshire from Rutherglen to Carstairs.

This would free up existing lines running through Motherwell and contribute to achieving Glasgow to London journey times of 3 hours 15 minutes.

An offshoot from this line connecting to Shotts in Lanarkshire would also achieve a much faster Glasgow to Edinburgh rail service.

The report also suggests that a new north-south railway running alongside the M90 would help to cut journey times between Edinburgh and Perth, Dundee, Aberdeen and Inverness by up to 30 minutes.

While upgrades to the West Coast Main Line between Wigan and Carstairs would also speed up journeys between Scottish and English cities and make the most of HS2, the high-speed line planned to run between London and the north of England.

HeraldScotland: The report outlines plans for a new high-speed rail link between Rutherglen and Carstairs

Reform Scotland Advisory Board member and former transport minister Tom Harris welcomed the report, and said its recommendations echoed much of what was suggested in a similar study by Reform Scotland.

"All of these proposals are very welcome and very well thought through," he said. "It is very similar to a Reform Scotland report where we talked about the absurdity of having longer journey times between Scottish cities than between Glasgow and Manchester.

"There is a real need to reduce these journey times and Greengauge 21 seem to have looked at that very seriously and made some good recommendations.

"However, the question is whether or not Network Rail can be funded properly to make the necessary changes."

The report by Greengauge 21 also outlines a need to move away from a "London-centric" model for the railway and look at the needs of other regions and devolved nations.

It also proposes a closer tie-in with bus services, including the creation of mini hubs at bus-rail interchanges.

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Mr Steer added: "What we have published today provides a wealth of new analysis on connectivity strengths and weaknesses across the country.

"We hope this report will show just what can be achieved by being prepared to think strategically."

Watchdog Transport Focus said that the main thing passengers want is a "punctual, reliable service that provides a seat and gives good value for money".

Director David Sidebottom added: "Any strategy to improve rail in Scotland must deliver on these priorities for passengers."