And out of the plane's left window you can see world's biggest advert

The world's largest advertising hoardings, measuring 20,000 square metres, or the size of three football pitches, are soon to appear in fields near the airport.

Entrepreneur Paul Jenkins is to display adverts printed on huge panels of plastic mesh attached to scaffold frames 18 inches off the ground.

His company, Ad Air, says the messages are designed to be seen best at heights of between 100metres and 400metres, giving passengers up to 20 seconds exposure as they fly over.

Advertisers will have to pay about £500,000 a year for each of the three poster sites near Heathrow, which is used by 67 million passengers a year. The first goods to be promoted this way are expected to be business and quality products and global consumer brands.

Mr Jenkins said: "People who use Heathrow tend to be more affluent so the ads will reflect that." Ad Air has tied up deals in eight European cities, as well as Los Angeles, Chicago, Dubai, Riyadh, Beijing, Tokyo and Seoul.

Mr Jenkins, who came up with the idea eight years ago, denied the adverts would be a form of visual pollution. He said: "We have been in extensive negotiations with Hounslow council, even though the law says we don't need planning permission in certain places because they are temporary structures on enclosed land.

"The sites will be surrounded by fencing and landscaping to ensure they are not visible to residents and passers-by and will not be illuminated. The ads are made from mesh to prevent the formation of ponds that might attract birds that could endanger low-flying aircraft."