The delayed opening of Crossrail will cost Transport for London an immediate £20m in lost fares this year, a City Hall inquiry was told today.

But the total impact of the failure to open the £15bn train line in December could cost taxpayers hundreds of millions of pounds, transport chiefs conceded.

An extra £300m to cover increased construction costs was allocated by TfL and the Department for Transport in July. TfL had expected to generate £146m in passenger income and £176m from commercial developments in the new stations in 2018/19.

Crossrail TfL budget 201819

Mayor Sadiq Khan today told the London Assembly he had ordered an independent investigation into the full financial impact of the delay.

The central section of the line, between Paddington and Abbey Wood via tunnels under central London, is now not due to open to “Autumn 2019“.

Mr Khan said he was only told on August 29 – two days before the public announcement – that problems with signalling and train testing meant the opening by the Queen on December 9 would have to be scrapped.

He faced accusations at the London Assembly meeting that he had lost oversight of the project. Tory assembly chairman Tony Arbour asked him: “Does that not suggest you were kept in the dark over the matter?” Fellow Tory Steve O’Connell said the delay was due to “incompetence“.

The Standard reported in January the serious concerns that Crossrail would blow its budget and open late.

Mr Khan said: “I’m extremely disappointed, frustrated and angry by the delay in the opening of Crossrail but I’m confident that, once completed, Crossrail will be both an amazing feat of engineering and a great asset for the people of London and beyond.”

Crossrail chairman Sir Terry Morgan was asked by Tory assembly member Keith Prince why he did not tell MPs, at a meeting in July when problems were known, that the opening date was in jeopardy. “I was not dishonest,” Sir Terry said. He said the December opening date was still the expectation at the time.