One of the requirements of the Digital Economy Act, passed yesterday in the "wash-up" before Parliament is dissolved, is that the analogue radio signal will finally be switched off in 2015.

The move is more controversial than the TV digital switchover, since an estimated 94% of radio listeners are satisfied with the analogue service, and even now less than a third of radios sold in the UK are digital sets.

Media regulator Ofcom has decided to redraw the licensing rules for digital radio operators in an attempt to encourage further spread of the medium.

Currently, the plan is for Channel 4 and its minority partners to take a 65% stake in Digital One, the lossmaking national platform that Global Radio inherited when it purchased GCap Media. Global and its network partner Arqiva, meanwhile, will take a stake in Digital Two, which Ofcom says may eventually become a national/regional hybrid transmission platform. Ofcom hopes Channel 4 will launch its three new stations on D1 by April 2009, although given the current advertising climate, only E4 Radio is fully expected to meet this deadline.

It looks as if Channel 4 may be quietly scaling down its big idea to launch ten new digital radio stations.

It was July 2007 when 4 Digital was awarded a national digital licence, but concerns over a potential lack of demand are blocking progress. The only other currently active multiplex is the one owned by Global Radio, and it only has three stations broadcasting although it has room for a further seven. Executives are starting to question the wisdom of launching a second multiplex when the first has not hitherto been as successful as hoped, and it is possible that Channel 4 may instead launch its stations on Digital One and take a stake in the platform.

The Digital Radio Working Group, set up last year by the government, and consisting of the BBC, commercial broadcasters, car manufacturers and the DCMS, released a report yesterday which suggested switching off the FM signal for all but the very smallest local radio stations by 2020.

Radio companies have been having trouble coping with the twin costs of broadcasting in two formats, and at the moment only 11% of radio listening is done via DAB. Many believe a more forceful approach could be useful. Culture Secretary Andy Burnham commented yesterday:

"I believe that radio must have a digital future if it is to remain relevant. I am pleased that the group has set a possible framework for digital radio migration."

Radio owners are meeting Ofcom today to ask it to reduce the burden of digital radio broadcasting. They say Ofcom has awarded too many multiplex licences and should withdraw some, and argue that the penalties for closing a digital service (including the automatic re-advertising of an associated FM licence) should be scrapped.

Digital radio in the UK could be stuck with an inferior system. Already, more than five million listeners have bought DAB radio sets, but DAB+ is cheaper and provides better sound quality.

Some commentators are suggesting that over the next few years many broadcasters could ditch the MP2 format used by DAB, making millions of sets obsolete. There are some technical details to be found here.

Ofcom - the UK's media regulator - has hinted for the first time that it might start switching off the analogue radio signal within five years, leaving 150 million analogue radio sets obsolete. Only five million digital sets have been sold. Ed Richards, head of Ofcom, said yesterday that without firm switch-off dates for AM and FM radio, listeners would be 'condemned to a hotchpotch of analogue and digital for decades to come'.

The Channel 4-led consortium of radio broadcasters, 4 Digital Group, which was awarded the the second national digital commercial multiplex last week, has promised to provide stronger competition to the BBC.

4 Digital Group is to spend £4.5 million marketing DAB technology over the next three years, with a further £25 million being used to promote the 10 national radio channels it will offer. Proposed stations include youth entertainment channel E4 Radio and speech-based Channel 4 Radio.