DELAYS and "staggering" cost increases to electrification on the Great Western Mainline have led MPs to call for review of rail regulation.

The House of Commons Public Accounts Committee said Network Rail – which manages Britain's rail infrastructure – had "lost its grip" on managing major projects, resulting in a "twofold blow to taxpayers".

The firm's plans for electrification – which include the tracks between Oxford and Didcot – are reported to have risen in cost from £1.6bn to £2.8bn in just a year.

And bosses admitted that targets for finishing the work were also "highly likely" to be set back, the committee said in a report published this morning.

The committee said the delays were also partly the fault of the Office of Rail and Road (ORR) and the Department for Transport, who signed off plans even though "the work could never have been delivered within the agreed budget and timeframe".

It called for a "fundamental review of the regulator’s role and effectiveness in planning rail infrastructure".

Meg Hillier MP, chairwoman of the committee said: "Network Rail has lost its grip on managing large infrastructure projects. 

"The result is a twofold blow to taxpayers: delays in the delivery of promised improvements, and a vastly bigger bill for delivering them.

"The potential near-doubling in cost of the electrification of the Great Western Line is a symptom of seriously flawed control and planning. 

"The government has identified rail infrastructure as a vital part of its economic plans and it is alarming that, in planning work intended to support these plans, its judgement should be so flawed.

"Passengers and the public are paying a heavy price and we must question whether the ORR is fit for purpose."

The Great Western Mainline includes the stretch of tracks between Oxford and Didcot, which was supposed to be electrified by 2016.

In its report, the committee said the Department for Transport was not in a position to update that schedule but had said it was highly likely the target would not be met.

Sir Peter Hendy, the chairman of Network Rail who was parachuted in earlier this year to undertake a review of its major projects, is expected to announce his findings next month.

The committees report added: "[Network Rail said] the review will ‘undoubtedly’ reveal further cost increases in the enhancement programme. 

"It said that there were “material cost challenges” on the electrification programmes and “significant cost pressures” in the wider portfolio of projects. 

"However, it claimed that by the end of the year (2015), it will have a “high level of confidence” in the forecast costs of its infrastructure improvement work since 85-90 per cent of the projects will have reached a key design milestone. 

"We intend to hold Network Rail to its claim that costs should be stable from this point."