The delayed Crossrail train link will not open until 2021 – and could be as much as £650 million over budget, it was announced today.

Crossrail bosses said the project would need between £400 and £650 million to top up to its £17.8 billion costs.

And chief executive Mark Wild confirmed that hopes the central part of the line would open in late 2020 were no longer feasible.

The rail link – also known as the Elizabeth Line – was originally due to open in December last year.

Once complete, it will connect Reading and Slough in the west and Shenfield in the east to central London.

It will also provide a new route to Heathrow Airport, and a link to Abbey Wood, on the border of Greenwich and Bexley.

Liberal Democrat Caroline Pidgeon – a former chair of the London Assembly’s Transport Committee – said today’s announcement was “appalling news for Londoners”.

She said: “For far too long Crossrail has made key decisions behind closed doors.

“It reports directly to both the Secretary of State for Transport and the Mayor of London.

“Sadly both have failed to hold Crossrail to account and to their budget. What have they found now that is increasing the costs even more?”

Ms Pidgeon said the delay would mean fresh uncertainty for businesses, while rising costs would jeopardise future investment in London transport.

A spokesperson for Sadiq Khan said the Mayor was “deeply frustrated” by today’s news.

He said: “Since the delay was announced last year, the Mayor has been clear he wanted the new Crossrail leadership to be fully open and transparent with Londoners about the huge challenges that remain around the project.”

He added: “Further work is taking place immediately to assess Crossrail’s latest cost estimates.

“Transport for London and the Department for Transport, as joint sponsors, will continue to hold the Crossrail leadership to account to ensure it is doing everything it can to open the line safely and as soon as possible.”