Rules governing how much the country's biggest commercial broadcaster ITV can charge advertisers will be adapted to suit the changing market but will not be removed, the competition watchdog indicated on Tuesday.

ITV had led a public campaign to see the regulatory system for its main channel changed, arguing it acted as a straitjacket which hampered innovation and taking risks because a drop in audience numbers could change advertising rates.

It said the system was no longer suitable in a fragmented market with so many channels.

The Competition Commission, which had already indicated it did not expect to drop the system altogether, said it would consult on widening the impact of the main ITV1 channel to include an ITV1+1 catch up channel and an ITV1 high definition channel.

"This has been largely supported by ITV and other parties," the Commission said. "We believe that this change will go a considerable way towards reducing the unintended costs to ITV of the current system."

Interested parties were asked to respond by February 2.