Labour Brexit divisions have spilled over once more after Diane Abbott became the third shadow cabinet member to declare she would campaign to stay in the EU over a deal negotiated by her own party.

In a move that heaps fresh pressure on Jeremy Corbyn, the shadow home secretary said she was determined to personally support Remain as it was the “best option for the country and my constituents”.

Her comments come after John McDonnell, the shadow chancellor, and Emily Thornberry, the shadow foreign secretary, both declared they would campaign for Remain against a Labour Brexit deal.

Labour has vowed to hold a fresh referendum if Mr Corbyn is elected, with the option to remain in the EU on the ballot paper against a Brexit deal.

But the public support for staying in the EU from senior shadow cabinet figures goes further than the party’s official policy.

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Ms Abbott told BBC Radio 4’s Today programme: “The party is committed to a referendum now and Jeremy has made that clear.

“If there is a referendum and if Remain is on the ballot paper – and there is every expectation there will be – I, like John McDonnell, personally will be campaigning for Remain.”

Asked if she would still back Remain against a Labour deal, Ms Abbott said: “I will be campaigning for Remain. I think Remain is the best option for the country and for my constituents.”

She denied Labour’s position was chaotic, saying Mr Corbyn would be guided by the party membership and the shadow cabinet over how to act.

Ms Abbott added: “I believe Jeremy will do what he has always done, which is do what he thinks is best for the country and the Labour movement.”

On Monday, Mr McDonnell said he believed that staying in the EU would be the “best choice”. Ms Thornberry said last month that Labour would be “off our bloody rockers” not to back Remain.

Meanwhile, the Labour leader has demanded the full publication of no-deal contingency plans after a leaked Whitehall dossier warned of months of shortages, chaos at borders and a possible recession.

Speaking as he prepared to meet business leaders to discuss the potential impact of no deal, Mr Corbyn said: “The government’s own Operation Yellowhammer dossier makes the chaos and damage that will be caused by Boris Johnson’s no-deal Brexit crystal clear.

“If the government wants to be believed that it doesn’t represent the real impact, it must publish its most recent assessments today in full. Boris Johnson’s denials can’t be trusted, and will do nothing to give businesses or consumers any confidence that the dire state of affairs described in these documents aren’t right around the corner.

“What we know for sure is that this government is wilfully committed to a policy that the prime minister and the cabinet know will destroy jobs, push up food prices in the shops and open up our NHS to a takeover by US private companies.”

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Elsewhere, Boris Johnson accused Mr Corbyn of wanting to “argue about Brexit for years”.

The prime minister wrote on Twitter: “I am committed to leading our country forward and getting Britain out of the EU by October 31st.