The BBC Trust has approved the launch of a free-to-air satellite service with ITV aimed at accessing digital TV.

The new service, Freesat, will be available to viewers who have been unable to access Freeview, the free digital platform. It was welcomed by campaigners for lower income and elderly households.

Currently Freeview, which is broadcast through terrestrial transmitters and aerials, is unavailable to reach 25% of TV viewers. Like Freeview, Freesat will require a one-off payment for the reception equipment.

The move was announced as the Office of Fair Trading raised "significant competition concerns" over BSkyB's acquisition of a 17.9% stake in rival ITV.

The OFT has recommended that BSkyB's holding in the commercial broadcaster is referred to the Competition Commission, while media regulator Ofcom added the deal raised "public interest issues" over news provision in the UK.

John Fingleton, OFT chief executive, said BSkyB's stake, bought for £940m in November, meant that ITV was "no longer fully independent".

He said: "Given the high stakes for tens of millions of UK consumers, we believe these risks to competition merit further examination."

Alistair Darling, Trade and Industry Secretary, has until May 26 to decide whether to refer BSkyB's stake to the Competition Commission.

The BBC Trust made the decision to launch Freesat after research showing 93% of respondents said the BBC should take action to improve access to its digital services in the lead up to digital switchover in 2012. The high definition-enabled service would provide an alternative to BSkyB and cable as a way of receiving digital channels and is expected to launch in spring next year.

Mark Thompson, BBC director-general, said: "The BBC's objective in launching Freesat is to support digital switchover by providing another way for licence payers to receive digital television channels and radio services, subscription free from the BBC and ITV.

"Its primary purpose is to drive digital take-up in analogue homes, particularly in those areas which are out of digital terrestrial coverage."

Michael Grade, ITV executive chairman, added: "Freesat will build on the success of Freeview by offering viewers a simple and cost-effective way of upgrading to digital TV.

"By filling in the current gaps in Freeview coverage, Freesat will ensure that a free-to-air, no strings attached option for accessing digital TV is available ahead of the digital switchover.

"By offering HD capability we will future proof Freesat if, as expected, high definition television continues to capture the imagination of viewers."

Help the Aged said Freesat would open up access to digital viewing to lower income and older households.

Currently, television viewers are able to access digital channels using BSkyB technology for free. However, the BBC said last night that the Freesat service was guaranteed not to incur charges in the future.