UPDATE: 1 p.m.
The BBC has a nice FAQ to help people prepare for Wednesday's strikes. In particular interest to travelers (and their agents), the site says that if delays occur, airlines must offer food and drink to passengers, and accommodation if necessary. But, the site adds, there will be no extra compensation because a strike is beyond airlines' reasonable control.
Anyone with a package holiday will have all elements of their break covered, such as hotels and cars.
And the bad news affects people arriving in the UK by boat, too: Ports could also suffer major disruption. Rights for ferry passengers are not as precise as for airline passengers. Terms and conditions on tickets outline people's rights, which usually include a refund or alternative sailing.
Generally, the site continues, ferry and airline passengers who are delayed, and made bookings for cars or hotels separately, must claim for any such lost "extra" bookings on their travel insurance. However, this cover will be valid only if the insurance was bought before the strike date was announced.
UPDATE: 10:55 a.m.
Reuters is now reporting that airlines are cutting flights into Heathrow because of fears of long delays and overcrowding when border staff join a mass strike on Wednesday.
Airports operator BAA, owned by Spanish infrastructure group Ferrovial, has warned of delays of up to 12 hours for passengers arriving at London Heathrow, which is Europe's busiest airport. It has asked airlines to halve the number of international passengers flying into Britain on Wednesday. Abu Dhabi's Etihad Airways on Monday said it had cancelled three flights to London's Heathrow airport on Wednesday and reduced capacity on another service, while Dubai's Emirates said it may be forced to cancel some services.
Heathrow's largest carrier British Airways, and Britain's Virgin Atlantic and bmi have encouraged customers not to fly into Britain on Wednesday and said they would allow passengers to switch flights to a different date free of charge.
Bad news for travelers to the United Kingdom this week: The UK Border Agency passport control will have to deal with long lines on Wednesday as agency and customs staff (along with other public sector employees) go on strike over pensions.
According to the Wall Street Journal, international airlines are taking steps to avoid "gridlock," rebooking passengers and considering cancellations. Airport operator BAA requested carriers at the world's busiest international airport to fly with half-full planes and warned of delays of up to 12 hours in processing incoming passengers.
BusinessWeek is reporting that passengers arriving at London Heathrow airport, Europe’s busiest, may have to wait as long as 12 hours to clear immigration. Cabinet Secretary Francis Maude has reportedly said that the government would, if necessary, use troops to “secure borders” and minimize disruption for travelers.