Boris Johnson insists May's Brexit plans are "substantially worse" than remaining in the EU.

The former foreign secretary renewed his attack on prime minister Theresa May amid speculation he plans to launch a leadership bid against her.

Johnson said May's Brexit negotiation had been "humiliating" for Britain.

His comments follow his claim that May had put a "suicide vest" around the country.

LONDON — The form of Brexit being pursued by Theresa May would be "substantially worse" than remaining in the EU, former Foreign Secretary Boris Johnson said on Tuesday.

Speaking at a meeting of the Brexit-supporting group 'Economists for Free Trade' inside Parliament, Johnson said that he would rather stay in the EU than allow May to pursue her plan of leaving Britain inside parts of the European Single Market.

"It seems to me there is this particular economic objection that in abandoning our seat around the table in Brussels and continuing to accept the single market legislation, we will be exposing UK businesses, manufacturers, entrepreneurs, innovators, to whatsoever rules the EU decides in the future to devise, even though those rules may well be inimical to the interests of UK innovation," he told the Economists for Free Trade group.

He added: "That seems to me to be a particular economic risk in Chequers and makes it substantially worse than the status quo."

Friends of Johnson have previously told journalists that he would rather stay in the EU than accept a 'soft' Brexit inside the EU Single Market or Customs Union.

Johnson reportedly told allies in January that any Brexit result which left Britain outside of the EU, but still closely aligned to it, would be a "total waste of time," adding that "I’d rather us stay in than leave like that."

The former foreign secretary today deflected questions about whether he planned to challenge May for the leadership, telling the meeting that "this is absolutely nothing to do with that, this is all about trying to change the position on the European Union negotiations, which at the moment I think are verging on the humiliating for this country."

However, his comments follow in the wake of a column he wrote for the Mail on Sunday in which he accused the prime minister of wrapping a "suicide vest" around the country, as well as widespread speculation in the press about an imminent leadership bid.