Philip Hammond has called for Boris Johnson to “moderate his language”, and described the current Tory government of radicals who seek Brexit by any means as unrecognisable from the party he joined.

The former chancellor said he would not attend the Conservative party conference – due to begin on Sunday in Manchester – for the first time in 35 years.

“The party I joined as a student [is] unrecognisable to me,” Hammond wrote in a column for the Times. “Gone is the relaxed, broad church coalition united by a belief in free trade, open markets, fiscal discipline, and a fear of the pernicious effects of socialism.

“The radicals advising Boris do not want a deal. Like the Marxists on the Labour left, they see the shock of a disruptive no-deal Brexit as a chance to re-order our economy and society. But I detect no appetite among our electorate for such a project.”

He said Johnson should “moderate his language and his demeanour” because “compromise requires reaching out, not slapping down”.

Hammond wrote: “Boris Johnson asserts, ever more boldly, that we will leave the EU with or without a deal. But as his sister has reminded us, he is backed by speculators who have bet billions on a hard Brexit – and there is only one outcome that works for them: a crash-out no-deal Brexit that sends the currency tumbling and inflation soaring.”

Meanwhile, it has emerged that the civil servant in charge of Brexit implementation has quit. Matthew Coats’s departure in the next few weeks is a blow to the government’s no-deal planning as he was also in charge of delivering frictionless borders.

He only took charge of the border delivery group in June after the departure of its previous boss, Karen Wheeler, who was tasked with ensuring customs, transport, immigration and security would run smoothly at all borders including airports, the Dover-Calais ferry route and – most sensitively – the Irish border.

Coats reported jointly to the Department for Exiting the EU and the Cabinet Office and headed a key unit in Michael Gove’s no-deal planning exit operations (XO) committee.

Hammond’s comments come after another former minister, Amber Rudd, said Johnson’s aggressive Brexit rhetoric could incite violence against opponents. Rudd, who quit the government and resigned the Conservative whip earlier this month in protest at the prime minister’s policies, told the Evening Standard she might stand in London as an independent Conservative at the next general election.

Johnson has been criticised for using words such as “surrender” and “betrayal” over Brexit. Rudd said she had been “disappointed and stunned” when the prime minister dismissed the fears of female MPs about a possible repeat of the 2016 murder of Jo Cox.

Asked about the Downing Street approach of couching Brexit as a battle between the people and a remain-minded parliament, Rudd said: “The sort of language [that] I’m afraid we’ve seen more and more of coming out from No 10 does incite violence. It’s the sort of language people think legitimises a more aggressive approach and sometimes violence.”

Rudd compared Johnson’s approach to that of Donald Trump during the 2016 US presidential election. She said: “The casual approach to safety of MPs and their staff [was] immoral,” and urged ministers to “consider their own judgments rather than be desperately loyal”.

Hammond wrote: “We will not be leaving the EU on 31 October. And the responsibility for that outcome, like the responsibility for the failure to leave on 29 March, lies squarely on the shoulders of those who have rejected the deal that has been on the table for almost a year.”