The HS2 chief executive's £46,000 bonus was linked to "control" of the high speed line's spiralling finances, it has emerged, despite the scheme's estimated cost almost doubling to more than £100 billion.

Mark Thurston, the highest-earning government official, received the payment on top of his £605,350 salary last year.

He has now revealed that the "key" criteria for the bonus included "annual control of our budget" and managing the scheme's schedule - which has slipped by up to seven years.

On Saturday Lord Berkeley, who helped lead Boris Johnson's review of the scheme, described the payment as "totally inappropriate", based on the information that has since emerged about the scheme's costs and expected delays.

Steve Baker, the former minister, called for Mr Thurston to pay the money back or give it to charity.

The Y-shaped line, which is due to run from London to Birmingham and then onto Leeds and Manchester, was given the go-ahead by Mr Johnson last month despite concerns about its costs and management.

The Prime Minister said costs "had exploded" and dedicated a minister to overseeing the scheme to avoid "further blowouts".

The bonus was paid to Mr Thurston in the 2018-19 financial year for his performance in 2017-18.

In the same period as the payment, HS2 Ltd, the government-owned firm run by Mr Thurston, warned ministers of "significant forecast cost increases and schedule delays".

Mr Johnson has since said that the scheme is likely to cost more than £100 billion, despite HS2 Ltd and Theresa May's Government maintaining that it was on target to meet its £56 billion budget. Last month the Prime Minister said HS2 Ltd had "not made the task easier".

Following a "stocktake" by Allan Cook, the new chairman of the firm, Grant Shapps, the Transport Secretary, also revealed that the line may not be fully open until 2040 - seven years behind its official schedule.

Lord Berkeley, who was deputy chairman of Mr Johnson's review of HS2, said: "Mark Thurston has not kept control of the programme or the budget, which changed significantly last year. This bonus is totally inappropriate."

Steve Baker, a member of the Treasury select committee and former minister, said: "On the face of it this bonus is ludicrous.

"HS2 is vastly too expensive, late, and running out of control. I think for decency's sake the chief executive could consider paying his bonus back or giving it to charity."