Kelvin MacKenzie will unleash all the venom he used to save for The Sun on Tuesday when he sues radio industry body Rajar.
The chief executive of The Wireless Group, which owns TalkSport, is instructing Queen's Counsel to pursue legal action against the audience measurement agency, which he claims uses outdated and inaccurate methods that deny it revenues.
The ebullient former editor of The Sun has run a lengthy campaign to persuade Rajar to change the way it measures listeners of radio stations around the country. The statistics are used to set advertising rates, so they determine the company's sales.
Rajar measures TalkSport's audience at two million while an alternative method using wristwatches, devised by market research firm GfK, measures it at seven million.
Rajar's method, which relies on a selected group writing down what they have listened to in a diary, is the industry standard. The Wireless Group estimates that it loses £15m a year in advertising revenue due to this method being used.
"We are not talking about it being slightly different; it is very much different," said Mr MacKenzie. "Someone has to decide this once and for all."
Rajar investigated whether to change its system, but decided against it last month. Its managing director, Jane O'Hara, confirmed that she has received a letter from The Wireless Group's solicitors asking for further information on Rajar's methods, but declined to say whether the group had consulted lawyers.
In its interim results, to be announced this Tuesday, The Wireless Group will state that it is taking Rajar to the High Court in London and will ask a judge to rule on whether Rajar should use the newer method to measure audiences. The outcome will be used to determine whether Mr MacKenzie will sue for damages to recover the money The Wireless group has allegedly lost.Reuse content