Only a handful of countries offer direct citizenship – but while some of them are tightening them up to stem inflows, others are making them more liberal.

The scale of citizenship programmes is perhaps hard to appreciate. Hong Kong was being flooded by people from mainland China, while Canada had 64,000 applicants pending last year when it decided to close the scheme (Quebec retained its own scheme).

But while a number of jurisdictions are reviewing their eligibility criteria and conditions, including Singapore, the UK, Australia and Switzerland, other countries like Latvia, Antigua and Bulgaria are anxious to tap even more of the growing demand.

The restrictions are not only coming from the granting countries: China and India are also seeking ways to stem the flow by restricting their citizens’ ability to hold more than one passport, and they – as well as South Africa – are also imposing currency controls, Nadine Goldfoot, a partner at Fragomen LLP in London, explained during the recent Finance Malta conference. The European Commission also has a say when the citizenship is granted by its member states, as this would grant them the same rights as any EU citizen. In fact, the Cypriot programme is being closely watched by the EU. Interior Minister Socrates Hasikos reported recently that the scheme, which initially cost €28m, then €10m, then €5m to join, had boosted the economy by €2 billion from property sales and investments.

With an estimated 13.7 million high net worth individuals around the world, even a fraction of these seeking a second or third passport translates into huge demand for citizenship programmes.

Henley and Partners citizenship expert Christian Kalin had told BBC News last year that he estimated that every year, several thousand people spend a collective €1.5bn to obtain another passport.