Zoe Ball bowed out in March

Ball left the show on 10 March to start a family with husband Norman Cook - musician Fatboy Slim - with her friend Cox, 25, taking over three weeks later alongside co-host Rajesh Mirchandani.

A Radio 1 spokeswoman said: "The audience share has risen quite considerably, which seems to mean people are listening to the programme for longer.

BBC figures

Radio 1: 11.31m (10.7%) - was 11.31m (9.9%) Radio 2: 10.0m (12.9%) - was 10.59m (13.3%) Radio 3: 1.95m (1.2%) - was 2.14m (1.4%) Radio 4: 8.98m (10.9%) - was 9.05m (10.9%) 5Live: 5.78m (4.1%) - was 6.18m (4.4%)

"It's especially impressive considering that Zoe left early and was replaced by Scott Mills before Sara took over, and with that sort of backdrop you would normally expect there to be a slight drop, if anything.

"This is very good news for Sara. She is off to present her shows from Ibiza this weekend and it's a great going-away present for her."

The show is listened to by 7.22 million people each morning, according to the Rajar figures.

They also show Radio 1's overall audience figures have remained static on 11.3 million, though its share is up from 9.9% to 10.7%.

Chris Evans: Disappointing showing for his Virgin show

But, with the exception of Radio 4, the BBC's other national stations all recorded falls in both their audience figures and their share of the market.

Overall, the Corporation leads the commercial sector, with a 51.1% share of the market.

BBC Radio & Music head of strategy James Tatam blamed Radio 5Live's tail-off on seasonal factors - despite the survey period including the station's Euro 2000 coverage.

"It could be the weather or anything," he said, adding the figures were more or less stable compared with the same period in 1999.

"We are very happy that we've bedded down at the levels we're at."

Commercial stations

Classic FM: 6.20m (4.4%) - was 6.26m (4.4%) talkSPORT: 2.01m (1.4%) - was 2.38m (1.4) Virgin AM: 2.91m (1.7%) - was 3.31m (2%) Figures show listeners and share for the quarters ending June and March 2000 Source: Rajar/RSL

Its rival talkSPORT showed a further drop in its audience, but the station's owners at The Wireless Group claimed its audience was getting younger and more affluent.

Chief executive Kelvin Mackenzie said it was "the audience we were going for".

Virgin Radio lost nearly 400,000 listeners over the three months, and Chris Evans' breakfast show was down by more than 100,000.

A spokesman said the news was "disappointing", adding: "This is a reflection of the Rajar figures generally, which don't seem to be pretty positive."

The Rajar figures are compiled on behalf of both the BBC and the commercial stations.

Commercial Radio Companies Association operations director Rachell Fox was pleased with statistics showing independent stations have a weekly audience of 76% among internet users.

She said: "This is particularly good news, as these listeners are likely to spend a greater amount of time surfing the net and less time using other media such as TV."