Letters released to ITV Cymru Wales by the Welsh Government show that a request to the Treasury for greater borrowing powers based its case for more money entirely on the rising costs of the proposed M4 relief road, a new motorway that would run to the south of Newport.
In his letter, Finance Secretary Mark Drakeford said that without prejudicing the outcome of the public inquiry, he wanted to explain why the project was going to cost more than originally envisaged.
The details of the project have been further refined, including enabling works too integrate Newport Docks with the M4 project ... Together with other factors such as construction inflation arising from the change in the start date, the costs of the project have increased from previous estimates ... The overall cost of the scheme is now estimated at £1.3 billion, excluding VAT and inflation.
It seems that Mark Drakeford needed to make a strong case, as the Chief Secretary to the Treasury, Liz Truss, pointed out in her reply that the Welsh Government had not yet used any of the substantial borrowing powers that it had already been given. But she agreed to let officials meet to discuss what could be done.
The Treasury still hasn't actually agreed to the extra borrowing powers but there seems to be strong support for the idea within the UK Government, notably from the Welsh Secretary, Alun Cairns, just so long as it means that the new motorway is built.