ER and Friends are among the UK's most popular programmes

Channel 4 chief executive Michael Jackson: "It is Channel 4 that has turned Friends and ER into such valuable and admired programming franchises in the UK."

He said the channel had agreed a deal "which protects the money and effort we have invested in making these shows some of UK television's most sought-after properties".

The new agreement is a big win for the channel - the comic lives and loves of the six American twenty-somethings in Friends and the hospital drama ER have been among its biggest draws.

Both series have attracted a regular audience of around 2.6 million viewers per episode on Channel 4 - for episodes already seen on Sky.

The deal could strengthen its bid to launch its own paid-for entertainment channel, E4.

However, Channel 4 is still in talks with Sky and may decide to allow the rival broadcaster an opportunity to screen the programmes because of Sky's position as a major force in distributing TV services.

Another alternative would be to sell on the rights to a third party.

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First-run Friends episodes have gained the biggest audiences for satellite and cable channels, regularly drawing over a million viewers.

But Sky Networks managing director Elisabeth Murdoch said the asking price was too high for a bought-in series.

"I have made it clear for some time now that our preference is to put money into the British creative community and develop new British franchises," she said.

Sky - which spends around �350 million a year on commissioned shows - will still be first to screen the sixth series of Friends next year but Channel 4 will have the rights to the next three seasons.

Both shows are made by Warner Bros and are the top two TV programmes in the US, where NBC recently paid $13m (�8.2m) per show for three more seasons of ER.