The board which runs the BBC yesterday set out to find what a digital Gaelic TV channel would be worth to viewers.

The cost of the service would be almost £18m a year, but the BBC Trust admitted that the value would be more difficult to calculate.

The Trust has now launched a Public Value Test, giving those with a particular interest, and the public at large, the chance to have their say on the proposals. The joint venture by the BBC and the government-financed Gaelic Media Service (GMS), if approved, would provide a dedicated Gaelic channel broadcasting for up to seven hours a day.

It would also include enhanced Radio Nan Gaidheal services and more internet content on BBC Alba. The Gaelic Media Service, a public body set up under the 2003 Communications Act to generate programmes, would put up £10.1m of the £17.9m annual cost, with £7.8m from the BBC. The BBC would also fund distribution costs, taking its total contribution to at least that of GMS.

The service would also receive programmes and promotions from Scottish Media Group worth £1.2m over three years, in return for an easing of SMG's peak-time Gaelic programming requirement. The BBC said the service was expected to appeal to Gaelic speakers and people who understood the language - about 86,000 people according to the 2001 census.

The Trust also predicts the service could reach nearly 10% of the population. If given the go-ahead, the service would be launched next March. Jeremy Peat, the BBC national trustee for Scotland, said the decision was not a foregone conclusion.

The proposal would have to fit the purposes of the BBC - sustaining citizenship and civil society, promoting education and learning, stimulating creativity and cultural excellence, representing the UK's nations, regions and communities, bringing the world to the UK and the UK to the world, and delivering digital services.

It will also undergo a market income assessment by the regulator, Ofcom, to determine whether any related services would be prejudiced.

With both the previous and present Scottish governments committed to Gaelic programming - to the tune of £11.9m a year - it now looks set to enter the digital age. It would include the news and weather in Gaelic. At least half of the funding provided by GMS would be spent in the independent sector.

Provision would begin next March on satellite and broadband, on digital cable later in the year, and - in Scotland only - on terrestrial TV with digital switchover between 2008 and 2012.

It would be free at the point of use, with no advertisements. Catch-up viewing would be available via BBC iPlayer.

The proposal says that the new service would make available a wider range of content than before, with genres including daily news and weather, sports, children's, teenagers' and young adult programming, music and entertainment, factual programming, and support for people learning Gaelic.

Margaret Mary Murray, the BBC's head of Gaelic, said that you would not have to be a Gael to enjoy Seirbheis Dhidseatach Ghàidhlig, even if you have trouble pronouncing it.

Going digital means it will be available with English subtitles, with no subtitles, and even - for those learning the language - with Gaelic subtitles.