Among those qualifying for help will be households with at least one person over the age of 75, or someone with a significant disability.

Legacy of choice

Ms Jowell announced the plans at the Royal Television Society conference in Cambridge.

"Digital television is no longer a probability, it is a certainty," said Ms Jowell.

"I believe it can leave us with a legacy of more choice, for more people, than anywhere in the world."

She said the government had taken the initiative to be "ahead of the curve" in introducing the technology, but added it was aware some people would need help.

Figures from media regulator Ofcom show that an estimated 63% of households in the UK already have digital television - up from 61.9% from the previous quarter.

The total number of households with digital television now stands at 15,715,178.

Future costs

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But Ms Jowell conceded that many of those yet to switch over to digital "are exactly the people that the State has a duty to protect".

The switch-over will enable the analogue spectrum to be sold off for other uses, as well as encouraging the public to take advantage of multi-channel television.

Switching off the existing analogue signal means every television and video recorder, in every room, must be connected to a digital receiver if it is to work.

Many people may also have to pay for a new aerial. This could prove a particular problem for the elderly and those on low incomes.

Support for vulnerable households would be funded by the BBC through the licence fee, said Ms Jowell.

Ms Jowell told the Cambridge conference that the switch-over would start in the ITV Borders region in 2008.

She said that the switch-off of the analogue signal would allow everyone to access all the digital services through an aerial, where currently only 73% of households have access and only 80% can watch Five.

Pilot scheme

David Sinclair, policy manager at Help the Aged, welcomed the announcement, but warned that in a recent survey, 57% of older people still saw digital television as a threat.

"Switch-over to digital television will inevitably be a confusing process for many people... the government has a job of work to do to make the case to older people in clear, easy-to-understand terms.

"Manufacturers and retailers also must rise to the challenge by developing technology and services which are accessible and innovative. "

In March, two villages in Carmarthenshire - Ferryside and Llanstephan - became the first in the UK to switch off their analogue signal after voting for the switch following a pilot scheme.