The Government has been accused of "betraying" rail passengers after scrapping plans to electrify three rail lines.
Labour and the Liberal Democrats criticised the announcement by Transport Secretary Chris Grayling setting out plans for new trains on the Midland Main Line, Great Western Main Line and in the Lake District.
The Department for Transport (DfT) said that because of new technology, the electrification works between Cardiff and Swansea, Kettering, Nottingham and Sheffield, and between Windermere and Oxenholme, will no longer be needed.
The DfT said modern "bi-mode" trains which can switch from electric to diesel mid-journey will be used on the Great Western and Midland Main lines, with passengers in Wales benefiting from new Intercity Express trains which will each deliver over 130 more seats and faster services.
Long-distance journey times from Nottingham and Sheffield will be reduced by up to 20 minutes in the peak, with the train operator in the Lake District beginning work to trial an alternative-fuelled train, it said.
Opposition parties seized on the decision not to complete electrification of the routes, saying voters had been 'taken for a ride'.
But the DfT said: "Passengers will benefit sooner and experience less disruption compared with putting up intrusive wires and masts along routes where they are no longer required."
Mr Grayling said: "We are making the biggest investment in the railways since the Victorian era and upgrading services across the country, including in Wales, the Midlands and the North.
"Passengers expect and deserve high quality rail services and we are committed to using the best available technology for each part of the network, delivering significant benefits for those who use our railways."
However, Liberal Democrat transport spokesman Jenny Randerson said: "This decision is a betrayal of passengers across the country who would have benefited from these upgraded routes.
"The Liberal Democrats secured vital investment for rail electrification when in government. That was then delayed by the Tories and now has been scrapped altogether."
Labour's Shadow Transport Secretary Andy McDonald said: "The Tories have been promising the electrification of the Great Western Mainline from Paddington to Swansea since 2012 and today's announcement confirms that they have been taking people for a ride.
"The cancellation of works means passengers will be denied the faster, greener, more reliable train journeys they were promised, and South Wales will miss out on the economic activity that improved rail services delivers.
"The decision betrays a promise to South Wales, and the Transport Secretary sneaking out the news on the final day before he goes on his summer holidays adds insult to injury."
Mick Cash, leader of the Rail, Maritime and Transport union, said: "This Government's talk of rail investment is just jam tomorrow when in reality important upgrade and renewal work across the UK is being shelved and scrapped due to on-going austerity."
Later, Mr McDonald led calls for the Transport Secretary to come to Parliament to defend the "disastrous U-turn", rather than "sneaking" it out on the last day of Parliament so MPs could not challenge the plans.
Raising a point of order in the Commons, he said: "Today, on the last day of the session, a statement has been sneaked out which is of massive economic detriment to the country, and lays waste to any semblance of industrial strategy, and totally conflicts with what was said on Monday night at the despatch box about electrification, and smashes to bits the Government's promises to the people of the North and the Midlands, and especially to the people of South Wales."
Deputy Speaker Eleanor Laing said it was not a matter for her to decide but assured MPs the message would be heard.
Manuel Cortes, leader of the Transport Salaried Staffs Association said: "The Tories' commitment to Wales, the Midlands and the Pennines is skin deep.
"To cancel the electrification of the line from Cardiff to Swansea is an act of economic vandalism. Our railways and the people of Wales both deserve far better than this."
Aslef general secretary Mick Whelan said: "It's yet another reminder of the lack of ambition for the future which has beset the railway since privatisation and confirms that the Government's rail policy is no more than make do and mend.
"Bi-mode trains are more expensive, less reliable and slower to accelerate than electric trains. Passengers on packed trains today will be on even more packed trains in 10 years' time."
Ken Skates, Cabinet Secretary for the Economy in the Welsh Government, said: "It is enormously disappointing that UK ministers chose to brief the press instead of Welsh ministers in advance of their decision to back-track on their promise to modernise the mainline in south Wales, and chose to try to bury this bad news at the very end of the parliamentary session.
"This scheme would have delivered significant and much-needed improvements to journeys between Wales' two largest cities and to the communities along the route.
"We cannot allow the UK Government to continue to renege on their commitments and disadvantage economic growth in Wales. Devolution of powers and a proportionate funding settlement in this area must now be progressed so that we can ensure that our rail infrastructure gets the funding it needs to deliver the fast, reliable and frequent services needed to support our communities and businesses, and to grow our economy.
"Although Wales and the Marches area has around 11% of the railway track in England and Wales, since 2011 the area has only benefited from around 1.5% of the money spent by the UK Government on rail enhancements.
"It is simply unfair that the people of Wales are repeatedly disadvantaged so that railway spending can be focussed on improvements which predominantly benefit the south east of England.
"Passengers in Wales experience poor network reliability, low speeds and capacity constraints which results in a much smaller proportion of people being able to choose to travel by train than in England and Scotland."
Ed Cox, director of the think tank IPPR North, said: "This decision will do very little to ease frustrations at the raw deal the North and Midlands get.
"IPPR North figures show London gets almost £1,500 more per head than the North for transport investment, and this lies behind the anger and economic injustice that fuelled the Brexit vote.
"We need to see transport decisions made by new, powerful regional government with teeth, as we see in most devolved nations, if we're going to rebalance the economy away from the over-heated London and the South East anytime soon."
Stephen Kinnock, Labour MP for Aberavon, said: "The Tories simply do not care about the people of Wales.
"Theresa May was able to find a £1 billion bung for the DUP to enable her to cling on to power, and she found £6 billion for high-speed rail in England, but when it comes to standing by her promises to the people of Wales on rail electrification, it's a very different story.
"Then there's the grubby, disgraceful way in which the Tories have sneaked this announcement just as Parliament is going into recess, thus enabling them to dodge proper parliamentary process, scrutiny and accountability.
"It seems that the UK Government has picked today as a good day to bury bad news - your typical Tory hit-and-run operation."
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