Television channels could be allowed to show an extra 20 minutes of adverts during some peak time evenings after regulator Ofcom launched a consultation that could result in public service broadcasters boosting advertising income by £85m per year.

The consultation is being launched as part of a review into TV advertising.

Viewers and broadcasters are invited to say whether there should be changes to the amount and length of commercial breaks.

Ofcom said its initial preference was for no change to be made to the overall amount of advertising, but promised to consider views on a range of options before making a decision.

The regulator is also inviting views on whether there should be changes to the rules on advertising during peak viewing hours, the number of commercial breaks and how much teleshopping should be allowed.

Stewart Purvis, Ofcom content and standards partner, said: "We want to ensure that viewers continue to benefit from a wide range of advertising-funded television services, and that the arrangements for advertising and teleshopping do not intrude more than is necessary."

Ofcom said that many viewers, broadcasters and advertisers had been opposed to more advertising.

The review follows the introduction of a new European directive - Audiovisual Media Services Directive.

This allows up to 12 minutes an hour of advertising.

Currently commercial public service broadcasters - such as ITV1, Channel Four, Five and S4C - show on average seven minutes an hour of adverts while non-PSBs, which include Sky One and E4, broadcast an average of nine minutes an hour.