Two of the party’s most senior ministers, Mr Maas and Frank-Walter Steinmeier, the foreign minister, held their own press conference to disown the decision within hours of its announcement.

“The special crime of insulting a foreign head of state is out-of-date,” Mr Maas said at the time. “The idea of lese-majeste no longer has a place in our criminal law.”

It later emerged the press conference had been agreed in advance as the price of the SPD’s acceptance of the decision.

But it appears the party is now moving to abolish the law outright.

Mrs Merkel committed her government to scrapping the law by 2018 even as she announced the prosecution of Mr Böhmermann would go ahead.

But the new legislation prepared by Mr Maas would reportedly overturn the law immediately.

It follows moves by the state governments of North Rhine-Westphalia and Hamburg to have the law overturned.

“I want to bring a Bundesrat proposal to abolish the offence of lese-majeste immediately. Then it would no longer be possible to convict Mr Böhmermann.” Thomas Kuschatsky, the North Rhine-Westphalia justice minister, said.