Figures produced by Rajar (Radio Joint Audience Research) show that although Radio 1's listeners still outnumbered Radio 2's by 11 million to 9 million in August, its share of listening hours fell to 12 per cent compared with 14 per cent for Radio 2.
The national commercial stations, Atlantic 252 and Virgin 1215, appear to have been the major beneficiaries, according to the information in Media Week.
Roger Gane, executive director of Rajar, said: 'These must be the informal figures produced for the stations. The next quarter's figures are not yet available so this must be information based on part of the period.'
The last set of quarterly figures for May, June and July, showed that Radio 1's audience had slumped to a record low of 12.1 million listeners, a fall of 3.4 million on the previous year. However, the slippage appeared to be slowing with just 876,000 defecting in the preceding three months.
Critics of the station have attributed the decline to the decision last year by Matthew Bannister, the station's controller, to axe ageing broadcasters such as Simon Bates and Dave Lee Travis in favour of a new generation of disc jockeys and an assortment of news and comedy.
However, Radio 1 had been losing listeners for several years, with 1 million deserting the station in the quarter before Mr Bannister took control. This was largely because of the Government's liberalisation of the airwaves which has seen Radio 1 move from enjoying a near-monopoly on pop to competing with 140 local broadcasters as well as Virgin 1215 and Atlantic 252.
In a speech earlier this week, Mr Bannister said that given the growth in commercial radio 'it would be foolish to suggest that . . . Radio 1 could continue to hold the audience levels it had in the past.'