London’s new multibillion-pound Crossrail service will miss its opening date by the best part of a year, a spokesman for the service has said.

More time is needed to complete “final infrastructure and extensive testing” for the 73 mile west-to-east express train line to ensure a “safe and reliable railway” is delivered, according to Crossrail Limited.

Services were due to begin running by the end of the year, but the central underground section between Paddington and Abbey Wood will now not be opened until autumn 2019.

Sadiq Khan, London’s mayor, called the delay “disappointing”.

Rail minister Jo Johnson announced last month that the scheme’s budget had been hiked by hundreds of millions of pounds, from £14.8bn to £15.4bn, due to “cost pressures”.

The railway is known as Crossrail during its construction phase but will become the Elizabeth line once services start running. Some 200 million passengers are expected to use it every year.

When it is fully opened, trains will run from Reading and Heathrow in the west through 13 miles of new central London tunnels to Shenfield and Abbey Wood in the east.

Crossrail 2, which will run north-to-south from Tottenham Hale to Wimbledon, is expected to open in the 2030s.

Crossrail Limited described its 10-year project – one of Europe’s biggest infrastructure undertakings – as “hugely complex”, stating that the original timetable for testing has been reduced by contractors needing more time to complete work in the central tunnels and develop software.

The firm insisted that “the focus remains” on opening the full line “as soon after the central tunnels open as possible”.

Simon Wright, Crossrail Limited’s chief executive, said: “The Elizabeth line is one of the most complex and challenging infrastructure projects ever undertaken in the UK and is now in its final stages.

“We have made huge progress with the delivery of this incredible project but we need further time to complete the testing of the new railway.

“We are working around the clock with our supply chain and Transport for London to complete and commission the Elizabeth line.”

A spokesman for Mr Khan added: “It is essential that a safe and reliable railway operates from day one, and this has to be the top priority.”

Labour’s Andrew Adonis, the former transport secretary and national infrastructure chairman, called the delay “more Grayling catastrophe”, referring to the current transport secretary Chris Grayling.

Andy McDonald, the shadow transport secretary, accused Mr Grayling of “going missing” after the announcement. “He should be explaining how the Crossrail delay happened and what he plans to do about it,” he tweeted.

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It follows severe criticism of Mr Grayling over the botched introduction of new rail timetables in London and the north of England, which saw a huge number of services cancelled earlier this year.

The Epsom MP was forced to endure a vote of no confidence after Govia Thameslink Railway and Northern left thousands passengers stranded in May.

The Department for Transport said: “We are disappointed by the delay to the opening of the Crossrail central section.

“However, the safety of passengers and staff and reliability of services is the overriding priority and we accept Crossrail Limited’s assessment that more time is needed to fully test the railway before passenger operations can commence.

“We remain confident that Crossrail will deliver a great improvement to passengers’ journeys once it is fully operational.”

Crossrail would eventually deliver £42bn for the UK’s economy, the department claimed.

Mr Khan also came under fire for the delays, with Conservatives in the London Assembly calling him “devoid of any financial credibility”.

Keith Prince, the party’s transport spokesman, said: “Sadiq Khan’s financial plans were hugely reliant on Crossrail opening on time, on budget and meeting incredibly optimistic passenger targets.

“But he was warned in February that budget and time overruns were very possible, yet he seemingly has no contingency plan in place. It is Londoners who will have to pay the price for his incompetence.”

The mayor’s freeze on travel fares had left Transport for London in the red, Mr Prince added.