Proposals for new routes and upgrades to reduce train journeys between London and Scotland to three hours have been outlined by the company behind the HS2 high-speed rail project.

New track could be built either side of the Pennines, or bypasses introduced on sections of the existing East and West Coast Main Lines where speed is constrained, according to a report by HS2 Ltd.

The cost of the suggestions range from £17 billion to £43 billion, although some improvements could be introduced in stages.

The UK and Scottish Governments have agreed that further work will be carried out next year to identify the options with the best business case.

It is hoped that the plans would ease congestion on cross-Border routes.

Journey times between London and Glasgow will be reduced from around four and a half hours to three hours 56 minutes when the first phase of HS2 opens in 2026.

From 2033 a second Y-shaped phase, taking the line to north-east and north-west England and beyond, will result in journeys from London to Glasgow and Edinburgh in around three hours 38 minutes.

Ministers: Scotland-London rail journey times 'will be cut to three hours'

HS2 Minister Robert Goodwill said: "Scotland will benefit from HS2 from the day it opens, with shorter journey times to London from the start."

He added: "This report looks at ways we can build on these improvements and I thank HS2 Ltd for this work. Together with the Scottish Government, we will be asking Network Rail to identify any options with a strong business case for consideration for inclusion in future plans."

Scottish Government Infrastructure Secretary Keith Brown described the report as a "major milestone".

He went on: "High speed rail will bring billions of pounds worth of benefit to Scotland's economy and an infrastructure project of this magnitude - possibly the biggest Scotland's ever seen - means jobs, investment, benefits for the economy and benefits for the environment.

"This plan will bring to life our target of three hours or less Glasgow and Edinburgh to London train journeys, which will lead to a significant move from air to rail, bringing big reductions in carbon emissions."