On Britain’s doorstep is a shantytown. Scabies is rife, bronchitis too. Families sleep in flimsy tents in bitter cold. Children play in mud and rubbish. The police don’t go in; they just watch from nearby bridges, swinging batons. Volunteers do their best, bringing food, clothing, tarpaulins; smuggler gangs do their worst, preying on people’s desperation.

How are we letting this happen? France and Britain each year patent more than 14,000 new inventions, support a joint population of more than 120 million people and help 20 million more out of poverty overseas.

The talent of our two nations drove the industrial revolution, the best medical advances in history, and the creation of the world wide web. It is not beyond the wit of our two great countries to solve the problem of Calais.

In the last few months, I’ve travelled to Beirut, Lesbos, and Calais – talking both to those who have fled their homes and to local authorities who are struggling to cope. This work isn’t intended to be party political – we want to build a consensus on tackling the greatest humanitarian crisis since the second world war.

Of all I’ve seen, Calais is the most depressing. It is only a small corner of the European refugee crisis, but it is a bleak one. Of the 1 million people arriving in Europe last year, just 5,000 have ended up in the Jungle in Calais, 3,000 more on a wasteland at Dunkirk – the equivalent of just 0.006% of the combined French and British populations. In contrast 5,000 people arrive on the Greek island of Lesbos every day. In Lebanon a quarter of the population is made up of refugees.

That is partly what makes Calais so troubling: it isn’t too big to solve. Yet no one has a proper plan to sort it out. Not the French or British governments, the UN or the big aid agencies.

‘Dunkirk in some respects is worse than Calais.’ Photograph: Carl Court/Getty Images

No one is doing assessments to identify refugees who need sanctuary or illegal travellers with safe homes they can return to. No one is delivering asylum. No one is enforcing immigration rules. And, most urgently, of all, no one is making sure that vulnerable people – especially children – get basic humanitarian aid and protection to keep them safe.

In the Jungle I met children – aged just 11 or 12, younger than my own – who are there alone. One boy bears scars across his face from the bomb that struck his home. And they are vulnerable – to cold, violence, exploitation and prostitution, and to death as they take crazy risks throwing themselves on to trains heading for Britain. One lone British volunteer is doing her best to look after them. Were this on UK soil, it would be illegal for local councils to leave children in danger like this.

Dunkirk in some respects is worse than Calais. Here Iraqi Kurdish families, many of them women and children, have been dumped by trafficking gangs on waste ground with no proper shelter or sanitation. Aid workers say it is worse than anything they have seen in Sierra Leone or Darfur. In Lesbos, despite the huge numbers arriving daily, at least a registration of some sort is taking place, and the families I met still had a sense of hope, having managed to reach Europe’s shores and leave the violence and persecution of Syria and Afghanistan behind them. But in the Jungle, from what I saw, there is very little hope left – only despair.

The British government’s excuse is to say it is a French problem and British intervention would make things worse, encouraging more people to come.

I agree that France has to lead action on its soil. But Britain’s refusal to engage is already making it worse, and makes it harder to get the comprehensive solution we need.

We have a moral responsibility not to turn our back on this bit of the Europe-wide crisis closest to our shores: people suffering from cold, infectious diseases, sexual violence and exploitation, many of whom have fled war and persecution. But it’s also in no one’s interest to have a lawless camp at our border that is easy prey for criminal and trafficking gangs – and potentially extremists – to exploit.

Nor is it in the prime minister’s interest, if he wants to persuade people to stay in Europe, to give the impression that European governments and cross-border cooperation are incapable of solving this problem.

Left to themselves, France won’t develop a plan to prevent people coming and risking their lives trying to cross. Their latest proposal, for a new camp at nearby Grande-Synthe, is a sticking plaster, and risks replicating the problems of Sangatte 13 years ago.

Last time it took a proper deal between France and Britain to sort Sangatte. It included bringing in the UN to do asylum assessments, immigration enforcement, improved joint security and a managed programme for refugees where many were supported in France but Afghan refugee families with British relatives could apply for sanctuary in Britain. The result was a massive drop in illegal immigration and years without major difficulties until the recent refugee crisis began.

We should learn from that now. What we need once more is a comprehensive British-French deal. Of course the elements will change. But it should include urgent humanitarian aid, a rapid programme of UN asylum assessments, and immigration enforcement. And it needs a plan to prevent people ending up in Calais.

I’ve argued before for the reintroduction of Schengen border checks to manage the flow of people across Europe, as well as safe, legal routes for refugees with close family in Britain to apply instead of travelling to Calais. And the government should sign up to the cross-party call to join Save the Children’s plan to help 3,000 abandoned refugee children in Europe – including those in Calais.

Europe faces an immense task coping with the consequences of hundreds of thousands being driven from their homes – in Syria and Afghanistan especially – by conflict and persecution. Let’s at least show that we and France can together solve the Calais problem.