Tony Blair and two former deputy prime ministers, Lord Heseltine and Nick Clegg, have launched a late plea to voters to reject “division, isolationism and blame” and vote on Thursday to stay in the EU.

After the tragic killing of Labour MP Jo Cox, they say the country is living in “worrying times” in which people must work together and unite, not pull each other apart.

Along with other senior politicians and figures from public life, they write that the country should seek unity, not division, remaining “a democracy where disagreements do not degenerate into incivility and where debate is not used to divide our communities”.

They add: “We have a chance as a country to reject division, isolationism and blame. To choose co-operation. For the future of our children, that is a chance we must take.”

EU referendum: reject division, isolation and blame. Choose co-operation | the big issue Read more

Among other signatories to the open letter, published in the Observer on Sunday, are Doreen Lawrence, the mother of murdered teenager Stephen; Caroline Lucas MP, former leader of the Green party; Sir Brendan Barber, former TUC general secretary; Shami Chakrabarti, former director of Liberty; Sir Richard Lambert, former CBI director general; and Craig Bennett, chief executive, Friends of the Earth.

In a reference to Nigel Farage and other Leave campaigners, they say that attempts to divide people into “us and them” have created the risk of a dangerously divided society. “That reached a new low last week when Nigel Farage posed in front of (and sought to make political capital from) a poster of desperate refugees, many of whom were children, stranded on the Slovenia-Croatia border,” the letter says. “But public life, whether in politics or elsewhere, should be about something else – something better.

“It should be driven by a desire to bring people together when it would be easier to tear them apart. A wish to build bridges rather than erect walls. A fundamental belief in the principle that we are stronger together than we are apart. This is the kind of Britain we all want to live in. Peaceful, tolerant, compassionate.” The cross party group says the country faces a “stark choice”, with Britain’s economy and place in the world at stake.

Yesterday France’s economy minister Emmanuel Macron said that Britain outside the EU would become “a little country on the world scale [that] would isolate itself ... at Europe’s border”. Macron told Le Monde: “Leaving the EU would mean the ‘Guernseyfication’ of the UK.”

But, the signatories write, the referendum will also publicise to the world what sort of country it has become: “There is something more fundamental at stake: the sort of country we are.”

Labour MP and Leave campaigner Gisela Stuart said a vote for Leave was not about dividing people but renewing the country’s democracy. In a statement on Facebook she writes that she too is determined to “eliminate extremism” but that this should not lead to the closing down of genuine debate.

She writes: “We have to be scrupulous about how we treat each other. Politicians and voters must reflect on the hate-filled language that too often scars our debates and passes for discussion on social media. Short of this bile, we must take care before assuming that anger turned up to maximum volume should be the default way to hold a political discussion. It is a difficult balance to strike and we must be wary of retreating to the blandness and consensus that serve only to blur the outlines of the issues.

“For some time now voters have felt that there is little to choose between the parties. Since 1997, politicians have been tussling over the centre ground with often only nuances … to tell us apart. As someone put it to me: ‘There’s little change in the menu; they’re just arguing over who will be the cook.’ This referendum could not be more different.”

Stuart, MP for Birmingham Edgbaston, adds: “For me, the underlying question is clear: are the people able to choose the governments that make their laws and to throw them out when they fail? I believe leaving the EU is the way to safeguard this precious right. At the same time, I respect those who take an opposing view.

“I will not be the only person thinking of Jo Cox on referendum day. She paid with her life, working for her constituents. Whatever the result on Thursday, we will have had the privilege of exercising a hard-fought-for right.”