A much-anticipated decision on whether to electrify the Great Western railway line to Swansea was today put back until the New Year.

The Assembly Government condemned the move, saying it was further proof that Wales had been "sidelined’’ by the coalition Government in Westminster.

As part of a major rail announcement, Transport Secretary Philip Hammond said there would be 2,100 new carriages on Britain's network by May 2019.

Commuter services on the Great Western route between London and Didcot, Oxford and Newbury will be electrified.

But Mr Hammond deferred a decision on whether the rest of the line to south west England and South Wales would go ahead.

The Welsh Office said the £1 billion upgrade to Swansea, announced by the previous Labour government, remained under "serious consideration’’.

Mr Hammond said discussions would be held "with the Welsh Assembly Government on the business case for electrification into Wales’’.

Confirming plans announced in the Chancellor's spending review, Mr Hammond said lines between Liverpool, Manchester, Preston and Blackpool would be electrified at a cost of £300 million. Work is expected to begin next year and to be finished in 2016.

He also committed the Government to funding "in its entirety’’ the cross-London Thameslink scheme, although it will finish two years later than planned in 2018.

Wales's governing Labour-Plaid Cymru coalition has tried to put pressure on the UK Government over the electrification of the line from Paddington to Swansea.

First Minister Carwyn Jones said: "This is a very disappointing announcement.

"Given that the electrification of the line is non-devolved - it is also very frustrating.

"The decision to proceed with this important project is solely a matter for the UK Government.

"Even if we had responsibility for the mainline, we would not be in a position to contribute any funding for this important project given the 40% cuts to our capital budget.

"We believe the business case for this investment - as it stands - is very robust, and will continue to make strong representations to the UK Government for this project to go ahead.’’ Deputy First Minister Ieuan Wyn Jones said: "This is yet another example of the UK Government sidelining Wales and avoiding their responsibilities to invest in our vital infrastructure.’’ Welsh Secretary Cheryl Gillan said: "We should not forget that the last government failed to electrify a single centimetre of track in Wales during their 13 years in office.

"They were, however, more than happy to make un-costed promises which committed the taxpayer to schemes costing hundreds of millions of pounds.

"This government is far more responsible when it comes to public money and it is right that we examine in fine detail projects such as electrification to Swansea.’’