The main line from London to South Wales is to be electrified as far as Cardiff over the next five years, the Government has decided.

The Labour Government announced in 2009 that it planned to electrify the line as far as Swansea but electrification was put on hold to allow for a Con-Lib coalition re-think.

The announcement to electrify to Cardiff comes three months after the coalition agreed to electrify the line from London Paddington to Didcot, Newbury and Oxford.

People in Wales are unhappy that the £704 million project will not provide for electric trains to run beyond Cardiff to Swansea.

Swansea West Assembly Member Andrew Davies told the Llanelli Star that the decision was a kick in the teeth for Swansea.

Transport Secretary Philip Hammond said there was not a business case for Swansea but Welsh Secretary Cheryl Gillan said the case for electrification to Swansea remained under review.

Mr Hammond also said: “We have established that a strong high-level case may exist for electrifying some of the Valley lines north of Cardiff.

“The Department for Transport will now work with the Welsh Assembly Government to develop a business case for the electrification of the Cardiff Valley lines.”

Ms Gillan said her department will work with the Welsh Assembly Government on a business case to electrify commuter lines north of Cardiff to Treherbert, Aberdare, Merthyr Tydfil and Rhymney, and to Penarth and Barry in the Vale of Glamorgan.

Robin Smith of the Rail Freight Group said: "We are pleased to hear that electrification of the Great Western main line is to proceed but are profoundly disappointed at the decision to end the wires at Cardiff and not electrify through to Swansea.

"This means that many key sites for freight in South Wales will not be able to benefit from electric traction."

The DfT now says rail electrification is an important part of its carbon strategy because an electric train emits between 20% and 35% less carbon per passenger mile than a diesel train.

The DfT adds: “This benefit will only improve as the electricity generation industry reduces its carbon levels. Electric trains also have zero emissions at the point of use, of particular benefit for air quality in pollution hot spots like city centres and mainline stations such as London Paddington.”

Network Rail will fund the electrification and is planning to use high-tech factory trains during overnight closures of less than eight hours to avoid disruption to passengers.