Plans for a £100 million investment in turning a surface coal mine near Ystradgynlais into a Global Testing Centre of Excellence for trains have taken a step forward.

Powys County Council’s planning committee approved an application by Celtic Energy Limited to adapt the land at the Nant Helen site, making it suitable for large-scale development.

Celtic Energy believe it could support a wide range of future uses including agriculture, woodland, nature conservation, leisure, tourism and employment – as well as the rail testing centre.

The plans take the form of two large looped land form platforms – although concerns were raised that building embankments above the village of Cae Hopkin and Brooklands Terrace could be dangerous because of drainage at the site.

Powys County Councillor David Thomas (Tawe- Uchaf, Labour), who called in the application, said: “This proposal is to put a huge embankment on top of what is already sodden and badly drained ground.

“We’re disappointed that the planning committee are not able to visit the site and view these concerns at ground level.”

Celtic Energy's agent Damian Barry, of Ove Arup, said: “The proposed earthworks are engineered to be stable in accordance to conventional rail and road embankments.”

Mr Berry added: “The Welsh Government intends to bring forward its application for a Global Centre of Rail Excellence in the next two months.

“If you approve this application today it will unlock an exciting next chapter for this site for the local economy and communities.”

Regional mineral and waste planning manager, Hugh Towns, said: “There is still a lot of work required before the embankment is constructed, there are a number of planning conditions proposed to ensure we understand exactly what the ground conditions are before any construction work is undertaken.

“The same goes for the related issue of water and drainage.”

Councillor Huw Williams (Ystradgynlais – Labour) said: “This planning application is being considered in the context of another application of international significance.

“It’s difficult to ignore that for the top end of the Swansea valley where there is a need for economic benefit.”

Cllr Williams wanted to see the residents of Cae Hopkin’s views on the embankment given weight and that more detailed discharge condition applications for the embankments and drainage would be discussed again.

Committee chairman, Councillor Karl Lewis (Llandinam – Conservative) added: “There is another opportunity to scrutinise the geotech (embankment) plans and the drainage.”

With this assurance the application was approved with 16 votes in favour and one abstention.