Christian Kälin, chairman of Henley & Partners, a consultancy, estimates that several thousand people spend a combined $2bn or more a year on adding a passport or residence permit to their collection. The largest sources of custom are China, Russia and the Middle East. Demand is rising fast, says Eric Major, who helped pioneer the industry while at HSBC, a bank. The number of clients from emerging markets whose net worth ranges from $1m-100m is growing at 15-20% a year, he reckons; for them, a few hundred thousand dollars is a bargain for the perks bestowed by an extra nationality. Instability is boosting demand: more South Africans are looking for second passports, for instance, because the number of visa-free destinations they enjoy with their own has shrunk under the prickly government of Jacob Zuma. So is terrorism: citizens of some rich countries (especially America) want a different passport when travelling or working overseas.