IT MAY seem like professional suicide to leave a radio show that pulls in 9m listeners for one with a meagre 400,000. But that is precisely what Chris Evans, the country’s most famous broadcaster and former hellraiser, did on September 3rd.

After 13 years at BBC Radio 2, Britain’s most popular station, Mr Evans is rejoining Virgin Radio, where he worked from 1997 to 2001. He was not the only broadcaster trading down in ratings this week. On the same day Eddie Mair, a former host of BBC Radio 4’s “PM” programme, hosted his first show in the same slot for LBC, a London-based station. More cuddly than hell-raising, Mr Mair has swapped 4m listeners at the BBC for about half that number.

That two of the BBC’s biggest radio stars have jumped ship for the commercial sector at the same time is no coincidence. Although Mr Evans was the BBC’s second-highest-paid presenter, with a salary of about £1.6m ($2.1m), he is likely to earn even more at Virgin; ditto Mr Mair at LBC. Both were embarrassed by having their pay made public last year, under new transparency rules at the BBC. But their moves also attest to the pull of an increasingly ambitious commercial sector. Stations like Virgin and LBC are on a roll. Messrs Evans and Mair want to be part of that.

Against many pundits’ expectations, the oldest form of modern mass-communication has held up well amid the din of television, streaming, video-gaming and all the other entertainments of modern life. In Britain, 90% of the population still listen to live radio every week. But it is commercial radio that has performed most strongly in recent years. Revenues from advertising plunged after the financial crisis of 2008, as did audience share. Both, however, have roared back. Commercial radio took a record £679m in ad revenues last year. It is now the fastest-growing medium for advertisers in Britain, with ad spending rising by 12.5% a year (against 5% for TV).

These sorts of figures have encouraged bosses to splash out on the likes of Mr Evans. In the first quarter of 2018 commercial radio stations got a record audience of 36m, running ear and ear with theBBC. LBC itself has increased its listeners from 1.1m in 2013 to about 2.1m today.

The switch to digital radio has helped. In 2010 there were 189 digital stations. Now there are 337. Digitisation has allowed local stations to go national, points out Siobhan Kenny of Radiocentre, an industry body. There were seven national digital stations in 2010. Now there are over 30.

LBC went national in 2014. It has been as successful at getting listeners outside the capital as inside. It has also pioneered a new kind of punchy political journalism. The station gives free rein to its highly opinionated DJs, of both the right (such as Nigel Farage, a former leader of the UK Independence Party) and the left (like James O’Brien, the Remainiacs’ hero). Political balance, as required by the regulator, is achieved by venting the full range of views throughout the day. This makes for more exciting radio than the BBC’s pernickety insistence on balance in every programme.

Mr Evans said of his leaving the BBC that he wanted to shake things up. He and Virgin should be well matched, for that is exactly what commercial radio is up to.