A report from the House of Lords Economic Affairs Committee says it is not convinced the £56bn budget is realistic and that major changes should be considered to keep costs down.

The report stokes up further doubts over HS2 with the Upper House committee urging the Government to consider a major rethink on the project.

This includes considering halting work on Euston station as the main terminus in the first phase, in favour of Old Oak Common in west London, which will connect to central London by Crossrail.

The Lords call for investment in the rail network in the north of England to be prioritised and warn that the Department for Transport’s  appraisal of the HS2 project is fundamentally flawed.

Lord Forsyth of Drumlean, Chairman of the Economic Affairs Committee, said: “As the Committee suggested in its 2015 report, rail infrastructure in the north should be the Government’s priority for investment, rather than improving north-south links which are already good.

“If costs overrun on the first phase of the project, there could be insufficient funding for the rest of the new railway.

“The northern sections of High Speed 2 must not be sacrificed to make up for overspending on the railway’s southern sections,” he warned.

The Lords committee, including two former Chancellors, a former Cabinet Secretary, former Permanent Secretaries to the Treasury and, a non-executive director at the Bank of England, urged that plans for Northern Powerhouse Rail be integrated with the plans for the northern section of HS2, with funding for the project ringfenced.

Lord Forsyth also warned: “The costs of HS2 do not appear to be under control.

“It is surprising therefore that the Government has not carried out a proper assessment of proposals to reduce the cost of HS2—such as lowering the speed of the railway or terminating in west London rather than Euston—which the Committee recommended in 2015.”

The Committee said it was concerned that the project would run out of money and the northern sections would not be built after former chairman of HS2, Sir Terry Morgan, told the Committee that nobody knew what the final costs of the project would be.

The report has been slammed by the High Speed Rail Leaders group which attacked calls for a project review as a recipe for wasting time.

A spokesperson for HSRIL said: “Parliament has approved the plans for HS2 and allocated the budget, investment is already happening and works have begun – are we seriously talking about ripping up the plans that businesses and local authorities have based their future on?

“We could not agree more that the North needs HS2 and that it needs to see those benefits soon. We cannot have further delays and we cannot have further prevarication over plans.

“HS2 is not an alternative to local transport projects – it is an essential component of them. Northern Powerhouse Rail can only reach its potential if we build HS2, something with which the political leadership in the north agrees.

“A complete reappraisal of the approach to building HS2 would be a complex, contentious and fruitless endeavour. The country, and particularly the north, don’t need more uncertainty from this parliament.”