A small table, two bottles of water and three topics to discuss. Pensions, Brexit and education. Nicholas Barr, Professor of Public Economics at the London School of Economics and Political Science (LSE), is an expert on Europe's great weaknesses.

The continent is ageing, the high birth rate of previous decades seems like a dream, and the pension pot in many countries is a purse at the end of the month. Growing old seems to be an act of resistance. Because part of the problem is brought about by the good news. We live longer and we live better. But the great challenge of an expanded existence is that it has to be financed. The International Monetary Fund (IMF) warned last July that pensions should only be updated by 0.25%, at least until 2022.

Barr has been studying this flammable space for years and his explanation is a tale of dominoes. The birth rate is falling and the labour force will be smaller in the future. "The only way for the economy to grow in this scenario is to increase the productivity of workers and this means more investment in physical capital and in education to finance savings". One piece pulls the other and a different world arrives. The minimum retirement age in two decades' time will be 75 ("more and more people will want to work beyond this age", he predicts) and workers will be able to decide whether to retire with their full benefit or receive a percentage and continue working. Retirement will be flexible. "If you have a long generation of pensioners followed by a small generation of workers, then pensions will be smaller and higher contributions will have to be paid". In 1999, people worked on average for 40 years and then retired for another 20 years, with every two years of work equalling one year of retirement. Today that arithmetic no longer exists.

Alone in the face of large population dynamics, each country pursues its own path. Canada, Sweden, the Netherlands and Switzerland have "excellent" pension systems, says the economist. On the other hand, Argentina had private funds, but the government nationalised them. A mistake. "There is no perfect, universal pension model. Each society has to find its own," he says.

This search is a painful process. The IMF admits that Spanish pensions will lose purchasing power. These days, the average pension represents 80% of the average wage. This ratio, warns the financial institution, will be lower in about thirty years' time. The consequence? Pensioners will have less purchasing power. Barr does not want to go into the Spanish case. "I don't know it well. But his uncertainties are similar to those of other European nations. In his opinion, all systems should be based on one idea. "Choosing a pension fund requires financial knowledge that very few people have. On the other hand, they do know whether they prefer to work full-time, combine retirement with a part-time job, or whether they want to retire at the minimum retirement age. These choices are simpler than selecting a fund. You have to design a system that doesn't force people to make choices, and if they have to make choices, give them simple choices.

There is a certain parallel in that view with Brexit. A simple choice (to leave or remain in the EU) that concealed complex consequences (depreciation of the pound, fall in growth) that few understood. Among the multiple readings that have followed, the Turkish economist Dani Rodrik - a friend of Nicholas Barr - warns of the "impossible trinity". The starting point is clear. "Democracy, national sovereignty and global economic integration are incompatible with each other," Rodrik warns. Do the British know this? Our debate before the referendum was absolutely awful. Society was misinformed, lies were told. The people who campaigned denied that trinity. They said: 'we can have all the benefits of the single market and we can control migration. And at no economic cost'. That is not the case. If you want to integrate into the European economy you have to give up sovereignty," Barr admits.

Terrible consequences

What will happen if the UK eventually leaves the single market? The consequences would be terrible, we will see a huge economic downturn," he argues. A reflection that leads to a fallacy. "There are those who believe there will be a downturn, but then we will grow faster. This is the same argument of the former communist countries of Central and Eastern Europe. But it took 15 years for Poland, which was the best performer, to recover its economic level. It is very optimistic to think that we will grow after such a sharp decline.

Those passing dark clouds also cloud education. The UK has the most expensive public universities on the planet, making it a financial mousetrap for many kids. Shouldn't the burden be eased? "It's not unfair to have university fees, it's unfair not to have them," he says. "If everything was paid for by the taxpayer then poor people would be funding the education of the rich. What stops poor people from going to university is not the fees, but that they don't do well enough in secondary school. The sentence, suspended in dialogue, requires clarification.

Barr argues that the key lies in the early years of education, and recalls a quote from Charles Clarke, former Labour Education Secretary. "If I were a true socialist, I wouldn't spend a penny on higher education; I'd spend it on early childhood education. That sentence shows how the funding of education is a serious problem in the UK. This economist has been arguing for 20 years for "the right design" of university loans. It is a model similar to that already applied by some business schools. The student gets a loan to finance his or her education, which is repaid with a percentage of his or her future income.