Image caption The £50bn HS2 network is not scheduled to be linked to Scotland

The economic case for the controversial high speed rail system HS2 is strongest when it is linked to Scotland, a report has said.

The Institution of Civil Engineers (ICE) Scotland "State of the Nation" report said transport investment is a key part of economic recovery.

But it highlighted Scotland's omission from the £50bn scheme.

It said failure to connect would risk a detrimental effect on inward investment.

The report said while Network Rail has forecast a doubling of passenger numbers throughout the UK within 20 years, some route capacity will be exhausted by 2024.

"HS2 has the potential to provide a step change in capacity and connectivity, delivering wider social and economic benefits and encouraging modal shift from air to rail," it adds.

But it warned these benefits would only be realised over longer distances.

Inward investment

"The case for UK high speed rail is therefore strongest when Scotland is included as part of the plans," according to the report.

"Failure to connect would leave it disproportionately further from key UK markets, and risks having a detrimental effect on inward investment, where decisions can be influenced by connectivity issues."

Currently it is planned to build a high-speed link between London and the West Midlands, with a second stage extending the network to Manchester and Leeds.

ICE (Scotland) called on the UK government to plan to extend the high speed line to Scotland.

The case for UK high speed rail is therefore strongest when Scotland is included as part of the plans. State of the Nation Transport Report, ICE (Scotland)

"An efficient, reliable and integrated transport network is vital to our economic growth and prosperity, connecting people with places and opportunity," said Ronnie Hunter, chair of the ICE Scotland expert panel which produced the report.

"We look forward to engaging constructively with Government to help address the challenges identified in our report and to build on the achievements we have seen to date."

Scottish Transport Minister Keith Brown welcomed the report.

He said: "The inclusion of Scotland now is crucial if the HS2 scheme is to realise its full economic potential.

"The Scottish government is committed to delivering the largest transport investment programme that Scotland has ever seen and this assessment of the performance of the transport networks plays a valuable role in that process."

ICE (Scotland) also sets out a number of proposals aimed at maximising transport's contribution to achieving sustainable economic growth for Scotland.

These include an urgent review of the impact of Air Passenger Duty (APD) and encouraging a debate around more contentious measures such as road-user charging.

It also wanted decision-making processes for transport infrastructure to be simplified to improve project delivery and increase investor confidence.