The data on the overseas markets comes from the International Passenger Survey (IPS) conducted by the Social Survey Division of the Office for National Statistics (ONS). The IPS has been running since 1961 and it aims to provide figures for the travel account of the balance of payments, for international migration statistics and for informing decisions on tourism policy.

The IPS is based on face-to-face interviews with passengers travelling via the principal airports, sea routes and the channel tunnel. In the 1999 survey 51,000 interviews were conducted with overseas residents departing the UK. The IPS sample is stratified to ensure it is representative by mode of travel (air, sea or tunnel) and port/route, with interviews conducted every day of the year.