Welsh transport minister, Ken Skates, has written to Chris Grayling for a guarantee that a no-deal Brexit would not disrupt South Wales Metro plans or the planned transfer of rail assets to the Welsh Assembly.
My Skates has made a written statement suggesting that the 'likely' need to allocate Department for Transport resources to cover further contingency planning around a no deal Brexit presents a risk to Welsh rail plans.
Last year, Whitehall transferred franchising authority for the new Wales and Borders franchise - starting from October 2018 - to the Welsh Government, with agreement on the funding arrangements.
Since the, the two side have been working on transferring the Core Valleys Lines (CVL) to the Welsh Government.
However Mr Skates said Brexit could put this work in jeopardy: 'I have been made aware in recent days that the increased prospects of a "no- deal" Brexit now threaten this asset transfer process, with potentially far reaching impacts for the wider delivery of the South Wales Metro project.
'As a result of the need to handle a ‘no deal’ Brexit in Whitehall, it is likely that resources within the Department for Transport will be moved from ongoing business within the department and on to other duties.'
He added that 'any reduction in the resources and capacity available within the UK Government to support the asset transfer puts not only the transfer programme at risk, but also jeopardises the deliverability of the South Wales Metro as contractually programmed'.
'I have written to the Secretary of State for Transport seeking his urgent guarantee that, this close to the end of the process, the CVL asset transfer will continue to be a priority for the UK Government.'
The CVL accounts for just over 15% of train miles in the Wales Route area and carries around 56% of all Wales and Borders passenger services each day.
Mr Skates also said that if a no-deal Brexit leads to a delay in the asset transfer and subsequently a requirement to re-programme the South Wales Metro infrastructure works, 'there is potentially a risk to the availability of the associated £159m European Regional Development Funding (ERDF), although I expect the UK Government Guarantee to stand'.