Chris Patten, the former Conservative party chairman, is to declare support for a second referendum on the UK’s membership of the EU.

The last British governor of Hong Kong will declare that a new public vote may be the only and the best way to prevent an act of “national self-harm” in the growing crisis over Brexit.

The declaration makes him the latest Tory grandee to emerge as a supporter of the People’s Vote campaign.

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Patten, who masterminded John Major’s general election victory in 1992, has previously opposed referendums as “fundamentally undemocratic”.

On Monday, he will tell an audience at a neighbourhood centre in south London that he has changed his mind since David Cameron’s historic decision to hold the EU referendum in 2016.

“The whole sorry shambles began with a decision to call a referendum in order to try to manage the English nationalist right wing of the Conservative party.

“It may be that we can only end this divisive and impoverishing argument by holding another referendum. That may prove to be the only and the best way for Britain to avoid an act of self-harm that would betray the aspirations of so many – not least the younger citizens of this country,” he said.

Speaking alongside Sam Gyimah, who resigned as universities minister last month over the government’s Brexit plan, Lord Patten will say that the government’s threat of a no-deal Brexit if it cannot get its way is an empty one.

He will say: “I don’t believe that the prime minister or many members of her cabinet think that this would be remotely responsible. It would be very damaging. These are similar to the tactics made famous by Dr Strangelove: if you threaten that something crazy will happen, your opponents will back down.”

Patten will say that further efforts to seek a compromise on the Irish backstop are unlikely to succeed. “No amount of verbal guff can deal with the real issue of the backstop. It is meant to be temporary. However you define that word, its temporary nature can only end when the 27 members of the EU agree this with the United Kingdom.

“In other words, the EU has the decisive say on what happens: that is called ‘taking back control’.”