Frankfurt is likely to overtake Heathrow as the world's premier international airport if, as is feared, the London airport's fifth terminal does not open until at least 2007.
The planning process to expand Heathrow is so far behind that even if a swift - and positive - decision is made once the public inquiry ends this week, Terminal Five could be six years late.
By that time Frankfurt Airport is forecast to have grown from its current annual passenger numbers of 40 million to more than 60 million.
Gwilym Rees-Jones, BA director of operational planning, said last week: 'If passenger traffic continues to grow at 5 per cent a year, by 2007 you are looking at Frankfurt becoming the world's largest international airport.'
Heathrow is bursting at the seams with 60 million passengers a year, and will stay that way until - if - Terminal Five opens.
Frankfurt, Paris and Amsterdam airports all have permission to expand to take 80 million passengers.
Domestic flights make Chicago O'Hare the largest airport in the world, but Heathrow is the world's busiest international airport thanks to its global flight network.
When the Terminal Five public inquiry ends this week, it will have been the longest in history, superseding the Sizewell B nuclear reactor inquiry in the early Eighties.
When it opened in May 1995 the Terminal Five inquiry was expected to take 18 months. If approval was given, it was thought that the terminal would open in 2001. But opposition by environmental groups and local authorities kept the developers at bay.
Even when the inquiry ends on Wednesday the inspector, Roy Vandemeer QC, is expected to take at least two years to complete his report. If this coincides with the run-up to the next general election, it could delay a final decision and push the terminal back to 2007 or even later.
Sir John Egan, BAA chief executive, said: 'Aviation is one of the few industries where the UK still leads the world. We have the world's leading international airport and airline [in BA] and it is vital that as we enter the next century we sustain this.'
