The conversation is one of hundreds of WhatsApp messages seen by BuzzFeed News that reveal the inner workings of the most influential lobbying force in British politics. Led by Jacob Rees-Mogg, the ERG has around 70 supporters on the Tory back benches and at least a dozen more sympathetic MPs in government. It dominates the Conservative party and has profoundly influenced Theresa May’s Brexit policy.

The huge leak — a major embarrassment for a group that prefers to operate out of the public view — reveals that, in addition to its extensive parliamentary and political manoeuvring, the ERG has waged a vigorous, nimble media campaign to shape the national conversation about Brexit.

The conversations reveal how an informal network of passionate, determined backbench MPs, with the support of only one paid researcher – his salary is funded by public money – and a free messaging app have worked the British media to make their case for a hard Brexit and push back against the Remainers they believe are trying to undermine the vote to leave the EU.

The ERG’s leaders, the chats indicate, regard winning the “air war” as essential to achieving their post-Brexit vision. After many years in Westminster, they’re acutely aware of the power of the media to shape the public’s thinking about policy issues and savvy about working it to their advantage — while also being deeply sceptical about the media’s motivations and convinced that some of the country’s top journalists are biased against them.

They work hard at managing the media. The ERG uses well-worn techniques adopted by professionally staffed campaigns to influence the coverage of their causes — centralised messaging, coordinated rebuttal, systematic complaining — but has elevated it to a level above that of most organisations in British politics, according to academics who reviewed the conversations at the request of BuzzFeed News.

Its members appear regularly on TV and radio programmes, are often quoted in newspapers, and produce a steady stream of articles for pro-Brexit publications like BrexitCentral and the Daily Telegraph. Behind the scenes, the MPs use WhatsApp to make sure they’re all on message, sharing consistent “lines to take” in response to journalists’ questions, providing briefings for its MPs before they do interviews, and circulating links to their members’ articles, appearances, and tweets.

“For political parties during election campaigns, this is standard practice using interns and volunteers,” said Steven Barnett, a communications professor at the University of Westminster, who reviewed some of the messages. “I can’t think of any previous example where it has been coordinated with such apparent dedication outside of an election campaign.”

Whittingdale, 58, is a considerable asset in this enterprise. A former culture secretary who chaired parliament’s culture committee for a decade, the Essex-based MP has extensive contacts in the media industry. He doesn’t have to ring a hotline or fill in an online form, like most Radio 4 listeners, when he hears something objectionable. He can contact senior executives at the country’s leading media outlets personally and know that his complaint will be taken seriously.

And so when Broadcasting House blundered on 31 December, Whittingdale went straight to one of the BBC’s senior executives to push for a correction. He contacted the corporation’s head of corporate affairs, Andrew Scadding, who said he would raise the matter, according to the leaked chats. Two days later, on 2 January, Whittingdale told his colleagues that Scadding had been back in touch: Broadcasting House had apologised to the guest for wrongly correcting him.

“I have said that I expect an on air retraction and apology,” Whittingdale said.

“Agreed,” replied Duncan Smith. The following Sunday, when Broadcasting House next aired, the programme’s presenter corrected his mistake.