The Welsh Liberal Democrats have raised concerns over the electrification of the Cardiff to Swansea mainline.
Electrification between Cardiff and Swansea was planned to be completed by 2018, however a report published in 2015 delayed the electrification of the line to 2024.
The total estimated cost of the Great Western route modernisation programme is £5.58 billion.
Commenting, former Wales Office Minister Baroness Randerson, said;
“It is becoming increasingly clear that the plans to electrify the Cardiff to Swansea mainline are in great doubt.
“We have already seen huge delays to the programme to electrify the line beyond Cardiff, and these further delays will mean years of uncertainty for Swansea and the wider region.
“Two years on from the initial delay announced in 2015 and there is still no clear costings, no start date and no budget. There is a very real risk that it will not happen at all.
“The UK Conservative Government must make assurances to the communities and businesses of the Swansea region. Delivering anything short of the original commitment would be wholly unacceptable."