Communications Minister Stephen Timms said that while direct marketing by phone can be a useful business tool, many firms just don't have the resources to cope.

"This measure gives those firms the option to say no to cold calls," he said.

Firms can block the calls by writing to the Telephone Preference Service (TPS) and registering the numbers that should not be called. Direct marketers will be responsible for checking the TPS before they make calls.

The Office of the Information Commissioner will enforce the measures. Breaching an enforcement notice could lead to a fine of £5,000 per offence in a magistrates court or an unlimited fine before a jury.

The move follows consultation with business organisations including the British Chamber of Commerce and Federation of Small Business. Firms can register their telephone numbers online through the TPS website.