Businesses are being warned they could be breaking the law if staff watch live TV on their computers when the firm does not have a TV licence.

Shops, offices and other workplaces could be fined up to £1,000, the TV Licensing authority says.

The law covers live transmissions online and does not apply to catch-up services such as those on the iPlayer.

If watching via mobiles and laptops that are battery operated, they will be covered by the owner's home TV licence.

The situation changes if equipment is plugged in - as it usually is in offices.

"At that point, you need a licence," said a spokesman for TV Licensing.

It has become an issue because there are more and more ways to watch television, the spokesman said.

"People can now watch on a PC or laptop, or even on some mobile phones and PDAs," he said, "and it's the responsibility of the business to make sure staff are obeying the law."