Conservative rebels planning to stop Boris Johnson’s planned cuts to aid spending could be thwarted if the Speaker rules their amendment to restore the 0.7% pledge is out of scope of the bill. Leaders of the rebellion said they had received expert advice that their amendment was in scope but Tory sources said Commons clerks had told the Speaker that the amendment to the advanced research and invention bill was not relevant to the matters contained in the bill. The Speaker has declined to comment until he speaks to the house. The planned rebellion, backed by at least 30 Conservative MPs including the former prime minister Theresa May and led by the ex-international development secretary Andrew Mitchell, follows the announcement last year that the amount of money spent on overseas aid would be cut from 0.7% of gross national income to 0.5%, amounting to a reduction of about £4bn. Ministers said this was necessary as a temporary measure – though they did not say for how long it would be in place – because of the economic damage from the coronavirus pandemic. Supporters of the amendment include the former ministers Jeremy Hunt, Karen Bradley, Tobias Ellwood, Johnny Mercer and David Davis, senior backbenchers including Bob Neill and Bob Blackman, and the 2019 intake member Anthony Mangnall. One rebel said they believed it was still “game on” until the Speaker made his final call. While 30 MPs are not enough to defeat the government, with support from opposition parties, the rebels were confident they could get at least 40 names. One former minister backing the bid said rebels would bring their amendment “at the next possible opportunity” if the amendment was rejected. “All this does is delay the inevitable. They know we have the numbers,” the MP said. Another rebel Conservative said they would be bitterly disappointed if the amendment was rejected. “Clearly it was drafted to be in scope and we took advice from the clerks to draft it,” the MP said. “My view is parliament has set in law 0.7% and parliament needs to have a say on the reduction to 0.5%. The government has been reluctant to test the will of parliament on this issue – arguably they are acting outside the law.” Mitchell said his amendment was a “totally in order new clause that reaffirms the promise that we all made just 18 months, every single one of us elected to the House of Commons, the promise we made not to cut aid”. He said: “Throughout all these seven months, the government has not been willing to bring a vote to the House of Commons, because they’re frightened they’re going to lose it, and I think they’re right, I think they’re very likely to lose it because those of us who made the solemn promise are not going to allow the books in Britain to be balanced on the backs of the poorest people in the world.” Johnson’s spokesman refused to say what personal lobbying of prospective rebels he was doing behind the scenes, only saying the government was waiting to see if the Speaker selected the amendment. He added ministers were committed to returning to 0.7% spending levels “as soon as the fiscal situation allows”. A Tory insider said the government chief whip, Mark Spencer, and Commons leader, Jacob Rees-Mogg, were applying “pressure” to suggest the amendment wasn’t in scope but were “not leaving it to chance” and remained “worried”. They said multiple undecided MPs were still getting personal calls from Johnson and Spencer, asking what it would take for them to support the government.