The divisions in the UK are so deep and pervasive that reconciliation could take a generation, Gordon Brown has said.

The country was facing competing visions of its future: isolated, inward-looking and disengaged, or open, outward-facing and internationalist, the former prime minister said.

Brexiteers want us to glory in isolation. Their vision is introverted and selfish | Gordon Brown Read more

Speaking at the launch of Christian Aid Week in Westminster on Sunday morning, Brown set out a passionate defence of the international aid budget and the importance of the fight against global poverty before addressing the themes behind the Brexit debate.

The UK had endured three years of “almost internecine division”, he said. The debate triggered by the Brexit referendum raised a fundamental disagreement about what it means to be British.

“And I’ll be honest, my worry is that the divisions in our country are now so deep and so pervasive that it could take a generation for us to reconcile these differences, bring people together and find a unifying vision of our country and a sense of purpose and direction that takes us forward into the modern world,” Brown said.

“Let us be honest – there are two visions of Britain that are competing with each other … There is one vision of Britain that derives from people’s misunderstanding of the Dunkirk spirit, this idea that we are better off when we stand alone, aloof and apart, sufficient unto ourselves, isolated if necessary, supposedly this independent spirit that means we are better off when we are disengaged from the world.”

He continued: “There is a second vision of Britain – a Britain that is open, outward-looking, engaged and not disengaged with the rest of the world, a Britain that is internationalist in its outlook, a Britain that sees it has responsibilities not just to itself, but that its national interest is served and also its moral standing is served by being engaged and part of the rest of the world.

“I believe this is a choice we have to make as a country. And I cannot see how the issue of our future can be resolved unless we understand that in a modern interdependent, interconnected world that to be outward-looking and not inward-looking, to be engaged and not disengaged, to be internationalist and not narrowly nationalist, is the only way forward.”

Brown described himself as “unapologetically in favour of being part of the EU”, but declined to be drawn on whether he favoured another referendum on Brexit.

The debate, he said, was “essentially between globalists and nationalists”. There needed to be a more effective counter-argument to the rise of nationalism, protectionism and populism. “If you have America first, India first, Japan first, Russia first, Turkey first, Britain first, then you have a world where it’s impossible to get agreements to do the things we need to do.

“We have to find a way of defeating the argument that the best way of running the world is every nation for themselves.”

Brown, who has a long record of tackling global poverty, dismissed arguments that the UK should cut back on its international aid budget. “We’ve got to argue back against people who say that aid is unproductive, aid is wasteful, aid is money going to the wrong people, aid is somehow inefficient, when all the evidence is that aid is well used and even more necessary if we’re going to deal with fundamental problems that no decent citizen in Britain would tolerate if they saw what was happening first-hand.”

He described Christian Aid as a “great British national institution”, recalling as a child being sent by his mother to distribute the charity’s red collection envelopes. Christian Aid hopes to raise £10m over the coming week, with 10,000 churches involved in fundraising.

“So much is achieved by people of faith and vision,” he said. “Social movements that bring about change are built on moral foundations.”

Christian Aid Week is focusing on maternal health in Sierra Leone, whose population of 7 million is served by 130 doctors and fewer than 1,000 nurses and midwives.