By Nick Higham BBC media correspondent

Phill Jupitus' 6 Music joins the Rajar system soon

Last week's radio listening figures for the first three months of the year will have made depressing reading at two of the big three commercial radio groups.

Both Capital and Emap saw listening fall at their flagship London stations, and Capital's share price promptly fell as well.

But for Emap, at least there was some good news. Though listening to Kiss 100 in London fell by almost a fifth, the station acquired almost a million extra listeners outside London for the first time - thanks to digital distribution.

And two new Emap stations, Kerrang! and Smash Hits Radio, also available only on digital, made their debuts with 770,000 and 760,000 listeners a week respectively.

This first Rajar radio audience survey to measure digital listening has proved that digital radio does have a future.

Not only the Emap stations but the BBC's Asian Network (weekly audience up from 150,000 for its traditional AM service in the Midlands to 433,000 once digital listeners are included) have shown that there is an audience for digital services.

But the speech station Oneword will have been disappointed to have recorded only some 50,000 listeners a week.

Most listening is still via digital televisions and, to a lesser extent, on the internet.

There are still only around 155,000 DAB (digital audio broadcasting) digital radios in total in the UK.

Freeview factor

Most digital radio listeners are using TV to tune in

Sky and Freeview and the cable networks NTL and Telewest all carry digital radio. But Freeview is especially significant, perhaps because it has far fewer television channels than Sky and so the radio services stand out more clearly.

The 1.4 million Freeview homes must account for the bulk of listening to the Emap services as they are not available on Sky.

Of course, listening to radio on the television is unsatisfactory in one important respect - TV sets are fixed in one place and much radio listening is done while on the move, whether in the car or around the house.

Ian Dickens, who runs the Digital Radio Development Bureau on behalf of the BBC, commercial radio and receiver manufacturers, says digital TV is a great way to "sample" digital radio.

He also believes it will stimulate sales of proper DAB digital radios so people can listen wherever they are.

The only problem with this - most DAB radios today are mains-powered, so hardly more portable than a digital TV.

Queuing up

The solid evidence that there is an audience for digital radio will also have commercial implications.

Until now, the operators have had to make do with anecdotal evidence that someone was listening, and whatever information they could glean from e-mails, text messages and phone calls.

Sonia Deol on the Asian Network - the BBC station has been a digital hit

Jim Freeman, head of radio at media buyer Zenith Optimedia, thinks advertisers will soon be able to buy digital-only packages of airtime.

Good news for them, he thinks, because of the tight formatting (and so tightly-defined audiences) of many new stations.

And good news for the likes of Emap, Capital and GWR, who have until now spent significant sums on digital services and digital distribution with little discernible return.

Now that Emap has dipped its toe in the water without getting its fingers burnt (as it were), other digital radio operators are queuing up to get their audiences measured as well.

Rajar boss Jane O'Hara says by October, her survey will include no fewer than nine national digital services, including all those broadcast by the BBC.