There are few better ways to understand the challenges of long-distance, international train travel than to arrive at an eastern European railway station to buy a ticket to a far-off point in western Europe. Try to buy a ticket for the Eurostar service from Paris and Brussels to London and the look from the other side of the ticket window is likely to be blank.

For years the problems have helped to keep the growth of passenger traffic on railways in most European countries and other parts of the world slower than that of air travel. Most airlines belong to smoothly-functioning, integrated ticketing systems. Since 90 per cent of passenger rail journeys are within one country, train operators have generally felt under less pressure to develop such systems.