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The UK government was not involved in talks with China over building the HS2 high-speed rail line, Transport Secretary Grant Shapps has said.

China's state railway company told HS2 Ltd it could build it in just five years and for less money, according to a letter seen by Building magazine.

But Mr Shapps told the BBC: "This has not been a discussion with the Department [for Transport]."

It comes after Boris Johnson this week approved the controversial HS2 scheme.

This was despite an official review warning costs could reach over £100bn, against a budget of £62bn.

When asked about the Chinese approach, Mr Shapps told the BBC's Andrew Marr on Sunday: "I've certainly had no advice on the subject. Obviously I will be asking to see what the communication has been."

He added: "This has not been a discussion with the department, it's been a discussion with HS2 as I understand it."

Under current plans, the final stretch of the line is not due to be completed until 2040 - although Mr Johnson has said he wants that brought forward to 2035.

However, Building magazine reported that the China Railway Construction Corporation (CRCC) had written to HS2 Ltd's chief executive last month, saying it could build the line by the middle of the decade, for a much reduced price tag.

The CRCC letter, also seen by the Financial Times, states: "We are certain that we can offer a cost that is significantly lower than the projections we have seen.

"The advantages are, in our opinion, too great to dismiss on the basis that there are obstacles to overcome.

"You will find that the Chinese way is to seek solutions, not linger on obstacles and difficulties."

However, British officials are said to be sceptical that it could operate in the same way in a democracy with property rights, protected landscapes and powerful lobbying groups.

Media playback is unsupported on your device Media caption HS2: Views from along the track

Conservative MP Tom Tugendhat warned that letting CRCC build HS2 would be "extremely questionable".

Mr Tugendhat, who is chairman of the foreign affairs select committee, said the UK was in "dire need" of a strategy around its relationship with China.

Mr Tugendhat told BBC Radio 4's Today programme on Saturday: "Have we decided to take back control from Brussels only to hand it over to Beijing?"

CRCC has transformed China's transport system, building most of the country's 15,500-mile high-speed network.

Supporters of HS2 say it will improve transport times, increase capacity, create jobs and rebalance the UK's economy.

Once it is built, journeys will be shorter. London to Birmingham travel times will be cut from one hour, 21 minutes to 52 minutes, according to the Department for Transport.

And while it is being built, it is expected to create thousands of jobs and provide a stimulus to economic growth.

In another BBC interview, Mr Shapps said he was planning a shake-up of the railways, with rail company franchises cut and a more centralised railway network system put in place to improve services.

"I think the current system is broken," he told the Pienaar's Politics programme.