The government's controversial plan for a Las Vegas-style supercasino and 16 regional casinos hung in the balance last night after David Cameron ordered his MPs to side with Labour rebels and Liberal Democrats in opposition to it.

The move is something of a volteface as last week the Conservative plan had been to back the Government's move to site the super-casino in Manchester as recommended by the Casino Advisory Panel, which rejected other contenders such as Glasgow and Blackpool. It could jeopardise Scotland's only regional casino, planned for Stranraer's harbour.

The change of heart from Tory high command appears to have been predicated on more evidence from a Lords committee which looked into the panel's decision. It showed the main reason for choosing Manchester was not economic regeneration, as most MPs and peers had understood, but on the ability to test "social impact" of gambling on the city.

The Tory leadership notified Tessa Jowell, Culture Secretary at the weekend, saying it would back the Government's plan only if the parliamentary order tomorrow covered just the regional casinos and omitted the supercasino. The upshot could be a vote on the location of the 16 regionals, as well as the Manchester plan.

Already 104 MPs, more than 80 of whom are Labour, have signed a Commons motion condemning the Manchester plan, expressing regret Blackpool did not get approval and calling for a rethink.