British Prime Minister David Cameron called the EU referendum to try to heal Conservative party divisions on Europe, but the bitterness of the campaign has sparked fears for its future — and his.

Senior Tories on rival sides of the debate have been attacking each other with increasing ferocity, with those backing a so-called Brexit even turning their fire on government policy to make their point.

The extent of the internal conflict has raised questions about how long Cameron, who was re-elected last year with a slim parliamentary majority, can survive regardless of the result on June 23.

Opinion polls point to a tight race, although the Cameron-backed campaign to “Remain” has a slight lead.

“The referendum may well break the Tories,” wrote Philip Stephens, the chief political commentator for the Financial Times.

While he said it had been a “delusion” to think the referendum would end decades of divisions on Europe, “the ferocity of the campaign has surprised even the realists”.

Philip Johnston of the Daily Telegraph added: “This civil war could destroy one of the most successful and enduring political parties the world has seen.”

Their comments echo those of veteran lawmaker Ken Clarke, a pro-European who served under Cameron and prime ministers John Major and Margaret Thatcher.

He warned the Tories were “dangerously close” to the splits over Europe that helped bring down Thatcher and dominated Major’s time in office, which ended with the party being cast into opposition for 13 years.

– ‘Lasting taste of bitterness’ –

Cameron wants to stay in the EU but has allowed members of his party a free vote, with the result that five senior ministers and 128 of the Tories’ 330 MPs are campaigning against him in favour of a Brexit.

A sixth eurosceptic minister, Iain Duncan Smith, resigned last month. He said it was a protest at welfare cuts but was accused of acting to boost the “Leave” campaign.

His subsequent attacks on the government opened the door for increasingly pointed arguments between other ministers, which stepped up with the start of the official referendum campaign this month.

Justice Secretary Michael Gove, who backs Brexit, accused Cameron’s side of peddling a “depressing and pessimistic vision” of a Britain that cannot survive on its own.

Finance minister George Osborne, a “Remain” supporter, accused those wanting to leave of being “economically illiterate”.

The intervention of US President Barack Obama on Cameron’s side with a threat that Britain would be at the “back of the queue” in US trade ties if it left the European Union did little to calm the situation.

Cameron’s decision to publish a document setting out the benefits of the EU using £9.3 million ($13.4 million, 11.9 million euros) of taxpayers’ money has also caused outrage among Conservative backbenchers.

Lawmaker after lawmaker stood up in the House of Commons to condemn the decision as an “abuse of public money” and a “crass move” that “will leave a lasting taste of bitterness and unfairness”.

– Cameron’s future –

Cameron says he will stay on whatever the result, no doubt to avoid turning the referendum into a vote on his personal record. He has already said he will not fight the next general election in 2020.

But veteran lawmaker Clarke said he “wouldn’t last 30 seconds” if Britain voted to leave the EU, and many commentators agree.

Philip Cowley, a professor of politics at Queen Mary University of London, said the question of how long Cameron could stay after a “Remain” vote depended on the tone of the campaign and the margin of victory.

“The Conservative party will survive, but it could easily hasten David Cameron’s exit from Number 10,” he told AFP.

He said tensions were high now because the polls were so close. If those backing Brexit feel they may lose, they may be more conciliatory.

“If it ended up being a 20-point margin of victory, then David Cameron would sail on quite happily,” Cowley said.

“If it is neck and neck all the way through, and it gets very heated, then even if we stay in he could be gone within a year.”

There is speculation that Cameron might reshuffle his cabinet after the referendum to bring in senior figures from both sides.

“To stay in No. 10, Cameron must reunite the Tory party after the referendum,” commented James Forsyth, political editor of the Spectator magazine.

“At the moment, he is not making that easy for himself.”