GREATER Manchester mayor Andy Burnham said it would "not be acceptable" if the north of England element to HS2 was delayed or made with only a "mix" of high-speed rail.

Responding to a widely leaked report about HS2's rising cost, the Labour politician told BBC Radio 4's Today programme: "I'm worried by the suggestion that there might be a delay in the North, or even that we might get some kind of second-class option, a mix of high-speed and conventional lines that it's talking about.

"And to me that would be the same old story. London to Birmingham, money is no object, and then all the penny pinching is done in the north of England.

"That would not be acceptable to me, and I'm sure wouldn't be acceptable to many other leaders across the north."

Mr Burnham said the development of an east-west rail route across the north - known as HS3 or Northern Powerhouse Rail - relied on HS2 being built.

"This isn't just about north-south rail," he told the BBC.

"The point about HS2 is it lays the enabling infrastructure for the east-west links that we crucially need and most people here would say that those are even more important.

"This is about building a railway for the north, right across the North, for the rest of the century.

"And that's why I don't support the idea that we will see downgrading of what is done north of Birmingham.

"That would be fundamentally unacceptable. If we get to a position where trains can go high-speed into Birmingham and then trundle their way north, then I'm sorry but that just isn't good enough."

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As reported by Press Association, the HS2 high-speed rail project could cost as much as £106bn, according to the official government review not yet published.

The review led by Doug Oakervee, a former chairman of HS2, reportedly says there is "considerable risk" that the project's cost will rise by up to 20 per cent beyond the £81bn to £88bn range set out in a report by current HS2 chairman Allan Cook just four months ago.

Mr Oakervee's review says work on phase 2b of HS2 from the West Midlands to Manchester and Leeds should be paused for six months to study if it could mix conventional and high-speed lines, according to the Financial Times, which has seen a copy of the paper.

The review says the Government should "on balance" continue with the 250mph railway, which would initially go from London's Euston station to Birmingham and then to Leeds and Manchester by 2040, but that this is subject to "a number of qualifications".

It says there needs to be "further work" done to assess HS2's impact on regional growth and it is "hard" to say what economic benefits will result from building it.

"Transport investment alone will not 'rebalance' the UK economy," the review adds.

Prime Minister Boris Johnson is expected to decide within weeks whether to go ahead with construction on the first phase of what would be Europe's largest infrastructure project.

The review said savings to the £106bn figure could be made by having the private sector contribute to funding HS2 stations, lowering specifications and improving the "cost performance of the management".

It also says that no other high-speed line in the world runs 18 trains per hour and recommends reducing it to 14.

A total of £8bn has already been spent on the HS2 project.