Johnson’s government has sought this month to pass laws that could override parts of Britain’s EU exit treaty that it signed in January, despite a warning from Brussels that doing so would wreck their future relationship.

But the Centre for Brexit Policy said this did not go far enough because the Withdrawal Agreement allowed Brussels ongoing influence in Britain over such issues as the law and state aid.

To boost British leverage, the group says the government should also threaten to impose punitive terms on those euro zone companies wishing to raise capital for investment in London.

John Longworth, director-general of the group, said he hoped its report would act as a wake-up call for ministers as negotiators hold talks on the future relationship in the final months before the Brexit transition period ends on Dec. 31 and Britain fully leaves the bloc.

Its publication is likely to increase the pressure on Johnson’s government to not back down in the tough approach it has taken to the talks. The group is backed by several key lawmakers across multiple political parties in Britain.

“Deeply embedded in the Withdrawal Agreement are sweeping powers for the EU over much of our commercial and national life,” Longworth said.

“The prospect of the European Court of Justice and the European Commission continuing to issue orders to the UK and endless legal wrangling truly means we face a nightmare on Brexit street unless we break free from their clutches at the 11th hour.”