Rajar sends out the information to broadcasters at 6am, five hours before it is released to the press and public.
Although there is no clear evidence the system has been abused, officials at the radio body believe circulating the figures the day before general release will give companies more time to prepare releases.
Capital, Emap, Chrysalis and GWR own the main commercial radio stations and leaked audience figures could be detrimental to their share prices in the volatile market leading up to the results.
Rajar was dealt a blow in a recent £66m court battle with Kelvin MacKenzie, the chief executive of the Wireless Group, after two of the biggest media buying agencies backed his push for an electronic audience measurement system to rival Rajar's traditional diary approach.
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