The transport secretary has accused London’s mayor of breaking election rules and “breathtaking political cynicism” by revealing the Crossrail opening date just a day before people in the capital head out to vote.

Grant Shapps claimed the announcement was an attempt to win favour in Thursday’s local elections and said he was referring it to the regulator, the Electoral Commission.

Political rules restrict what communications activity can take place in the run-up to an election.

The Tory minister described the announcement as an “unscrupulous headline grab” and said the government had “poured billions into Crossrail to solve delays clocked up on the mayor’s watch”.

Mr Khan, a Labour Party member, replied “he can do what he wants to do” when asked if he was concerned about Mr Shapps’ referral.

The mayor said the line’s opening was the “most significant addition to our transport network in decades” and would give “a massive economic boost” to London as well as the UK as a whole.

Crossrail, known as the Elizabeth line, will open on Tuesday 24 May, Transport for London confirmed on Wednesday – but it will be more than three years late and billions over budget.

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It will run from Reading in Berkshire to Shenfield in Essex and Abbey Wood in southeast London.

It was originally planned to open in full in December 2018 but it was hit by numerous problems including construction delays and difficulties with signalling.

It is hoped the Queen – who the line is named after – will be involved in the opening.

The line will operate 12 trains per hour between Paddington and Abbey Wood from Monday to Saturday 6.30am to 11pm.

Further testing and software updates will take place on Sundays.

The Sunday closures will be lifted on 5 June to help people travelling in the capital during the Platinum Jubilee weekend.

Andy Byford, TfL’s commissioner, said: “I am delighted that we can now announce a date for the opening of the Elizabeth line in May.

“We are using these final few weeks to continue to build up reliability on the railway and get the Elizabeth line ready to welcome customers.

“The opening day is set to be a truly historic moment for the capital and the UK, and we look forward to showcasing a simply stunning addition to our network.”

The project went massively over its original £14.8bn budget in 2010.

The total cost of the project has been estimated at £18.9bn, including £5.1bn from the government.

Mr Khan also said the Elizabeth line would make London “safer, fairer, greener and more prosperous”.

Liverpool Street to Ealing Broadway: 19mins (currently 32mins)

Tottenham Court Road to Heathrow Terminal 4: 39mins (currently 61mins)

Woolwich Arsenal to Canary Wharf: 5mins (currently 22mins)

Stratford to Bond Street: 14mins (currently 22mins)

Tottenham Court road to West Drayton: 32mins (currently 42mins)

He said it would “revolutionise travel across the capital and the South East – as well as delivering a £42bn boost to the whole UK economy and hundreds of thousands of new homes and jobs”.

Mr Khan added: “Green public transport is the future, and the opening of the Elizabeth line is a landmark moment for our capital and our whole country, particularly in this special Platinum Jubilee year.”

A full timetable with direct trains running across the Elizabeth line is expected to launch by May 2023.

Bond Street Elizabeth line station will not be ready to open on 24 May but is expected to be completed by the end of the year.

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