Plans to electrify the Great Western Mainline from Cardiff to Swansea have been ditched by the UK Government.

The decision not to electrify around 60 miles of track between the two cities, comes after the Westminster government earlier this week awarded £6.6bn worth of contracts as part of the next phase of the high speed rail network between London and Birmingham – as well as confirming the route for future phases to reach both Manchester and Leeds.

Electrification of the Great Western Mainline from Paddington to Swansea was promised by the then Tory government of David Cameron back in 2012.

But its delivery through Network Rail has been hit by delays – and seen its cost overrunning by some £1.2bn in the space of a year.

While electrification is on track to reach Cardiff by late 2018 or early 2019, a decision of whether to electrify the track to Swansea was put back for consideration in Network Rail’s next five year investment spending period for 2019-24.

Today’s decision means it will not be taken forward by the current government. And as a stand alone projection, at a later date to electrification reaching Cardiff, many feared it would fail, as has proven the case, the Department for Transport return on investment assessment.

However, writing for WalesOnline, Transport Secretary Mr Grayling said journey times between Cardiff and Swansea will not be affected, as new bi-mode trains – which will switch from electric to diesel at Cardiff Central Railway Station – will be just as fast as if the section was electrified.

And he said once the line is fully electrified from London to Cardiff, it will shave 15 minutes of current journey times between the capitals, compared to current diesel fuelled rolling stock.

Mr Grayling said: “Introducing the new fleet means all the benefit of electrification between Cardiff and Swansea, but without the months of work, the track closures and the dreaded rail replacement buses. It also means less noise and disruption for communities living near the route.

“The speed limit on the Swansea-Cardiff route is such that the new fleet of trains will be doing the route in exactly the same amount of time as they would be on a fully-electrified route. So it means the things people care about most (getting there on time and finding a seat) are delivered without the bother of what they care about least (how their trains are powered).

So that’s my pledge to the people of South Wales – a faster, smoother, more comfortable, more efficient, more modern journey between Cardiff and Swansea – but without the needless disruption of engineering works.

“And that’s why I’m pleased to announce today a whole package of improvements for the service, which will mean faster journey times within Wales, but also onwards to Bristol and London.

“They will also see passengers travelling in greater comfort, with more than 130 extra seats on individual trains and 40% more seats on rush hour journeys between Swansea and Cardiff.”

The new fleet of bi-mode trains will become operational on the Great Western Mainline from this autumn, although operational they are less efficient, heavier and more costly to run than electric only rolling stock.

Mr Grayling said he has also asked Network Rail to look at how journey times and connections can be improved in north Wales.

He added: “I’m also asking them to look at improvements to Cardiff and Swansea stations and to ensure services from Pembroke Dock to London via Carmarthen are on new, state of the art Intercity Express trains.”

The cost of upgrading Cardiff Central Railway Station, to cope with a projected huge rise in passenger numbers over the next few decades has, been put at least £100m.

The cost of electrifying the line between Cardiff and Swansea, based on the overspend to date on the project between London and Cardiff, could run into hundreds of millions of pounds.

As a non-devolved matter the Welsh Government will have little appetite, understandably, to fund it from its own budget.