A railway line that connects the south of Powys to major destinations in South Wales and England needs £20m worth of investment to deliver on its potential, a rail expert says.

Professor Stuart Cole said he felt the Heart of Wales Line was not delivering on its potential, but could do so at a cost of around £20 million.

He has submitted a report to a UK Government-commissioned review into what can be done to improve connectivity within the UK to help increase productivity and tackle social deprivation.

The Heart of Wales Line stops at towns including Knighton, Llandrindod and Llanwrtyd, en route to Shrewsbury, which links to the West Midlands and also north - via Crewe - to Manchester and Liverpool. It is mainly single track, with four daily services each way, although two of them currently run to and from Carmarthen rather than Swansea.

Prof Cole, who is chairman of the Heart of Wales Travellers' Association, said he believed there should be extra passing routes and a two-hourly services each way throughout a 12-hour operating day. He also felt the current rolling stock should be modernised to cater for cyclists and visiting families, with flexible ticket options and more integration with the Traws Cymru bus network.

"This can bring economic growth by encouraging people to travel to the area, where the biggest sources of income are tourism and agriculture," said Prof Cole.

"Walking and cycling are very important activities in Carmarthenshire and Powys. People come for the open air."

Prof Cole said flexible fares would allow tourists to go back and forth on the Heart of Wales Line and also use Traws Cymru buses.

He added: "The opportunity is there to get the kind of train which is suitable for cyclists, for families and groups. The rolling stock does need an improvement."

The emeritus professor of transport at the University of South Wales also said 87% of all journeys made into mid-Wales were made by car, and that a more connected and frequent train service with fewer interchanges for passengers coming from England would reduce that.

The UK review is being led by Sir Peter Hendy, the chairman of Network Rail. An interim report was published in March. Although it didn't mention the Heart of Wales Line, Prof Cole said the response he had received to his submission "seemed very positive".

Transport for Wales, which operates the Heart of Wales Line and Traws Cymru, said it planned to run an extra train from December, 2022.

A Transport for Wales spokesman said: "We're currently in the process of refurbishing the Class 153 units that we use on the Heart of Wales Line, providing a better experience for our customers. We have plans to significantly improve provision for cyclists on trains on the route – we’ll have more details on this soon.

"With regards to integration with bus services, we're working on plans to achieve this in the future, as part of the Welsh Government’s aspiration to create a more integrated public transport network."