Tony Blair and Theresa May have been embroiled in a public row after she accused him of “undermining” the EU divorce talks by calling for a second Brexit referendum.
Here, Sky News looks at the views of former prime ministers and ex-party leaders on Britain leaving the European Union.
:: David Cameron
Mrs May’s predecessor triggered the referendum on Britain’s membership of the EU and campaigned for Remain, before leaving politics shortly after the historic vote came back for Leave.
Speaking to Sky News earlier this month, he said he did not regret calling the referendum but added: “Obviously I’m very concerned about what’s happening today but I do support the prime minister in her efforts to try and have a close partnership with the European Union.”
:: Gordon Brown
The most recent Labour politician in Number 10, Mr Brown said Brexit had left the country divided and led to a breakdown of trust within the electorate.
He has also said the sense of betrayal felt by some of the public risks creating a “poisonous and toxic atmosphere” that could be exploited by populists.
In October, Mr Brown predicted a future referendum on Brexit will take place if Britain leaves the EU without a deal in March 2019.
He added that he expects an extended transition period, retaining some aspects of membership and that the next general election will be fought on Europe.
:: Tony Blair
The former PM said Mrs May must stop “banging (her) head against this brick wall” and go for a second referendum.
Mr Blair described the “disentangling” process of Brexit as “hideously complex” and said all options of leaving the EU have “significant drawbacks” compared with staying in.
After Mrs May robustly told him to step back from Brexit, he responded: “In these circumstances it is not irresponsible or insulting to put forward an alternative way to achieve resolution.
“The sensible thing is now to allow parliament to vote on each of the forms of Brexit canvassed including the prime minister’s deal. If they can’t reach agreement then the logical thing is to go back to the people.”
He continued: “What is irresponsible however is to try to steamroller MPs into accepting a deal they genuinely think is a bad one with the threat that if they do not fall into line, the government will have the country crash out without a deal.”
:: Sir John Major
The former prime minister who took up the reigns after Margaret Thatcher’s resignation has made several public comments on Brexit.
He has called for Article 50 to be revoked to give politicians across the Commons time to work through what he termed the “morass”.
He also warned that Brexiteers responsible for persuading the British public to leave the European Union will never be forgiven for their “false promises”.
:: William Hague
The former Tory leader has backed Mrs May’s withdrawal deal, saying if others in his party do not support it then “Brexit might not happen at all”.
Lord Hague has made it clear he believes a second referendum would be bad news for the country and has downplayed claims that the UK would be left in a difficult position in the eventuality of a “no-deal” scenario.
:: Iain Duncan Smith
Former Conservative leader Iain Duncan Smith turned Tory rebel said the PM should take a tough line with EU leaders by threatening to withhold the so-called divorce bill of up to £39bn agreed as part of the UK’s departure.
Mr Duncan Smith is resolute that the Irish backstop issue must be resolved, urging Mrs May to “say to the EU now ‘your £39 billion is fully at risk. We are not committed to the £39bn unless we get some resolution’.
“They know that this backstop can be completely replaced by an open borders policy. Push them to the point where they recognise they have to do that and it resolves everything.”
:: Michael Howard
Firmly against another vote, Lord Howard has said: “A second referendum would be a gross insult to the people.”
The former Tory leader has previously said the UK should look to leave the EU with a managed no-deal Brexit. Once out, the UK could then attempt to organise a free trade deal from the outside, he says.