Digital TV is due to replace analogue completely by 2010

In a report to Culture Secretary Tessa Jowell, it called for "clear and unambiguous incentives" to ease the nation's transition from analogue TV.

It said "greater certainty" should be given over the timing of the switchover - set for between 2006 and 2010.

The government said there were no plans to help fund the cost of replacing the UK's 35 million analogue TVs.

Ofcom set out 23 recommendations, including phasing in the switchover region by region and a mass national advertising campaign to build public support.

Under plans to speed up the process, the BBC and Channel 4 could face bills running into millions of pounds to broadcast from 2006.

Analogue spectrum

Ofcom said bringing the publicly-owned broadcasters in line with commercial rivals would "sharpen incentives" to encourage viewers in making the switch.

ITV has said it currently pays �225m a year for its licences to broadcast on the analogue spectrum, while Channel 5 pays �25m.

Proposed changes would see public service channels, including BBC and Channel 4, also being charged to broadcast for the first time.

The government has not set a specific date for analogue switch-off. Some industry observers have suggested this would be a political risk before a general election.

About 30% of households cannot receive digital terrestrial TV, and there is a suggestion the government could potentially alienate millions of voters.

A spokeswoman at the Department of Culture, Media and Sport said it welcomed Ofcom's report and would take "careful note" of its recommendations.