The future of HS2 hangs in the balance following the shock referendum vote to leave the EU.
Construction work on the Birmingham to London fast line is due to start next year but now, according to Hodge Hill MP Liam Byrne, "all bets are off".
With both the Conservative and Labour parties in disarray after the vote, leadership contests, a possible general election looming and talks to leave the EU set to drag on, there is a high risk the Government will call off the £50 billion HS2 investment until the future economic outlook becomes clear.
The HS2 track and train maintenance depot was due to be sited in Mr Byrne's constituency on part of the former Alstom and LDV site. He said: "There's red flashing lights all over this.
"There are different exit plans being talked about and if we take the wrong path there will be a hole in the budget."
He said that, with government borrowing now at record levels, an expensive project like HS2 could easily be sacrificed if the cost of Brexit or economic downturn hit the Treasury's finances.
Below: Birmingham politicians react to Brexit vote
Despite the six years and millions spent on planning HS2, it could easily be dropped, he said.
He added: "The HS2 Bill has not passed its final stage with the House of Lords yet. "If we get a general election in three to six months, it might not get through. I doubt we will see HS3 at all."
The city's future growth, particularly the delivery of major regeneration schemes at Curzon Street and Smithfield in Birmingham city centre, and UK Central at the NEC and airport, is closely linked to the development of HS2.
Prime Minister David Cameron and Chancellor George Osborne have been huge supporters of HS2. But now with one resigned and the other unlikely to remain in post long, their successors may not be as keen or could pull the project altogether.
Tory leadership front runner Boris Johnson has previously stated only lukewarm support for HS2, in part because there is opposition in his Uxbridge and South Ruislip constituency which is on the route.
The West Midlands Combined Authority has also been promised £4.4 billion in government money over the next decade to build transport links around HS2 - such as the new Midlands Metro lines and reopen the Camp Hill Chords and Sutton Park rail lines.
HS2 is not the only major infrastructure project under threat following the referendum. The third runway at Heathrow and the nuclear reactor at Hinckley Point are also at risk