The plans for the Great Western Main Line will see the lines between London Paddington, Reading, Oxford, Newbury, Bristol, Cardiff and Swansea electrified within the next eight years at a cost of £1bn.

Electrification of the Great Western Main Line could also affect the location of the western terminus of the Crossrail east-west London rail line. “With electrification now to be extended to Reading, it would be possible for Crossrail to operate to Reading, rather than Maidenhead, from the outset, and this option will now be considered by the Government and Transport for London,” the DfT said.

The line between Liverpool and Manchester via Earlestown will be electrified in the next four years at a cost of £100m.

Detailed planning would start straight away on the Great Western Main Line work, the Government said, with early engineering work taking place between 2012 and 2014 and the bulk of the engineering being carried out between 2014 and 2016.

“As with other rail investments, the cost of electrification will be funded by Network Rail and supported by the Government,” the DfT said. “Over the medium term this £1.1bn investment in electrification will be self-financing, paying for itself through lower train maintenance, leasing and operating costs. This means that this investment can take place without reducing already planned infrastructure enhancement work.”

Conservative shadow transport secretary, Theresa Villiers, said electrification would help reduce carbon dioxide emissions but added: “Gordon Brown is living in a fantasy land if he thinks this comes for free, without any cost to the taxpayer. Yet again Labour are maxing out Network Rail’s credit card, leaving the taxpayer to foot the bill.”

“After Lord Mandelson announced cuts in the transport budget [LTT 3 Jul], how can we believe that Labour can announce £1.1bn of new spending without impacting on existing transport commitments or putting further strain on public finances already stretched to breaking point?” Villiers added. “Gordon Brown needs to come clean about what current transport schemes could now face cuts to pay for today’s announcement.”

The Liberal Democrats also expressed some scepticism. “The transport secretary will argue that these electrification schemes are self-financing,” said transport spokesman Norman Baker, “and it is true that the figures do show them covering their costs, albeit over 40 years.”

Baker also expressed surprise that the Midland Main Line had not been chosen for electrification, either instead of or in addition to the Great Western Main Line.

“The incremental costs of electrifying the Midland Main Line are, in fact, lower than elsewhere, given that the line already has wires as far north as Bedford,” he said.

The Government’s position on the Midland Main Line is that work is ongoing to assess its potential for electrification and that the Great Western Main Line has been given priority in part because the fleet of Intercity 125 trains operating on the line is due to be replaced en masse in the next few years, which is not the case with the Midlands line. “Rolling stock fleets tend to last 30-40 years, so the replacement of the Intercity 125 fleet over the next decade creates a ‘once in a generation’ opportunity to electrify the route.”