The House of Lords last night voted against the government order on casinos, leaving culture secretary Tessa Jowell struggling to claim plans are "very much alive".
Peers voted 123 votes to 120 for an amendment sending the government's entire casino package back to the planning stage.
MPs approved the plans, despite initial expectations the vote would be too close to call. However, without support from the Lords, ministers have still been left contemplating their next move.
In an earlier interview Ms Jowell said the government had "no plan B" if parliament rejected the order and last night the culture secretary said: "Ministers will want to reflect and come back to this elected house in due course with proposals as to how to take this policy forward."
The Prime Minister's official spokesman agreed ministers would find a way to proceed with the plan. He said: "As Tessa Jowell told the Cabinet, this policy is very much alive.
"Ministers will want to reflect on where we are. What nobody should be in any doubt about is the intention."
The government had claimed it would be wrong to "cherry pick" the Casino Advisory Panel's recommendations and had asked parliament to approve the Manchester super casino and 16 smaller casinos as one package.
However, as she is unable to bring the same order to the Commons for six months, it is possible Ms Jowell could split the package, asking the Lords to approve the less controversial smaller casinos first.
Shadow culture secretary Hugo Swire said "it would be unthinkable for the government to attempt to bring back these proposals." He warned ministers not to ignore the concerns expressed over super casinos and accept the need for parliamentary scrutiny of the location and likely impact of the first super casino.
Ms Jowell accepted the Lords amendment, calling for a joint parliamentary committee to scrutinise the government's plans. This concession helped her win backbench support in the Commons, aided further by a three line whip.
More than 100 MPs, including 83 Labour members, had signed a parliamentary motion expressing their "surprise and regret" the Casino Advisory Panel recommended rejected Blackpool's bid to host the first super casino.
In an effort to gain their backing, the culture secretary had offered a generous regeneration fund for Blackpool, as well as hinting the seaside resort could be awarded a super casino in the next parliament.
With Ms Jowell's concession and a three line whip, the Commons approved the government's plans by 274 votes to 250. This has led some to suggest the government ignored dissent among the Lords to shore up Commons' support, with last night's defeat marking only the third time peers have voted against a government order.
Many Labour peers abstained yesterday with 105, around half the party's number, backing the government order. They were joined by 30 Conservative peers who had been given a free vote. Some 12 Labour peers backed the Liberal Democrat's delaying order.
It is unclear when the culture secretary will be able to return the order to the Commons. The house rises today for the Easter recess and would be barred from debating the issue on its return by purdah, which restricts the Commons from discussing locally sensitive issues in the run up to the May local elections.
It is expected the chancellor Gordon Brown will take over as prime minister soon after and he is thought to be less supportive of the casino plans, with insiders pointing to the 50 per cent tax rate he announced for super casinos in last week's Budget.