BBC Three is to become an online-only channel from the start of 2016 in a major blow to Daniel Radcliffe and Steve Coogan, who campaigned to keep it on the airwaves.

The BBC Trust approved the plans on the condition that, among other things, the BBC's main channels (BBC One and BBC Two) will air more shows aimed at the 16-to-34-year-old demographic.

"We know young audiences are already moving towards the online future, but we do recognise that in the short term some of them will feel the impact of the BBC Three proposals," said Rona Fairhead, the chairman of the BBC Trust.

But the governing body of the BBC rejected a proposal to create a new BBC One+1 channel, warning that the move would harm Auntie's commercial rivals.

The decision will by a disappointment for Coogan and Radcliffe, who were among hundreds of stars that pushed for BBC 3 to stay on the box.

The comedian and actor signed a letter with 750 other protesters to keep the channel on digital terrestrial TV.

"Disastrously, the closure and move online will remove at a stroke a vitally important outlet for new talent and innovative ideas, where some of the most successful and influential names currently working in British television were given their first chance," the document read.

BBC 3, which was launched in 2003 and is known for shows like Gavin & Stacey, will only be available on the BBC's online viewer, iPlayer, from next year. The BBC has said that move will save the broadcaster around £30m ($47m) a year.

"We welcome the Trust's provisional conclusion, which is the next step in delivering our vision for a new BBC Three," a BBC spokesperson said.

"With a frozen licence fee and the BBC's income cut by 26% we have had to make some very difficult choices. However our plans will allow us to innovate with new ideas and new forms of content for younger audiences. We'll now consider the areas the Trust have asked us to address and respond in due course."