Cadwalladr, 48, is a London-based features writer for The Observer. Before gaining prominence for her blockbuster reporting around politics and tech, Cadwalladr received plaudits as a novelist. In 2006, her debut book The Family Tree was made into a BBC Radio 4 drama. Many believe that her non-traditional CV has enabled her to attack her investigation with an unconventional and effective tenacity.

Her singlemindedness made reporting partnerships uneasy. Cadwalladr began working with media partners in September last year – six months before the story broke into a worldwide scandal.

Originally, the idea was to have Cadwalladr be the face of the programmes as a presenter.

Beyond a common non-disclosure agreement made with Cadwalladr before viewing some of her source material, ITN never reached a commercial agreement with the journalist.

One of the issues between Cadwalladr and ITN, and never resolved, was Cadwalladr’s prolific tweeting. She’d gathered a huge online following for long Twitter threads, speculating about parts of the unfolding investigation into Russia’s influence in 2016 election and Brexit referendum.

Producers wanted Cadwalladr to sign up to Channel 4 News editorial policies for the duration of the investigation, which would also see her abide by their social media guidelines.

Unlike newspapers and websites in the UK, Channel 4’s reporting would need to abide by the broadcast regulator Ofcom’s rules on balance and objectivity. Lawyers saw Cadwalladr’s tweets as potentially putting the undercover-part of the Cambridge Analytica investigation at risk of breaching these broadcast regulations. She never signed up to the social media guidelines or editorial policies.

“My social media output was flagged by Channel 4 as a concern but neither it nor any aspect of the editorial code was ever a point of dispute,” Cadwalladr said. “To the contrary, I was happy to contractually agree a two-week period of prior approval of tweets as requested. It is categorically untrue to suggest otherwise.”

Nevertheless, things quickly soured. With Channel 4 deploying a crew undercover, a meeting with executives and lawyers came to the conclusion that Cadwalladr shouldn’t be the face of the resulting programme. “There was a spectacular bust-up in November,” one source said, “From then on, Carole got really angry she wasn’t being kept in contact with what they were finding out undercover.”

In a column from November about the trolling and abuse she’d received from her reporting on Russia and Brexit, Cadwalladr referenced colleagues who had asked her to pull back from tweeting.

“Maybe you should be less noisy, a well-meaning colleague suggested,” she wrote. “As if I’d committed the journalistic equivalent of wearing a short skirt and asking to get raped. You risk looking biased, he said.”

It was at this point that Cadwalladr tried to ditch Channel 4 News for the BBC.

She tried to get the BBC’s Panorama programme to be her broadcast partner for the Brexit component of the investigation. BuzzFeed News has spoken to senior sources at both the BBC and Channel 4 News who saw this move as as a ploy to get the news organisations to fight over access to the story.

A BBC source said Cadwalladr had placed “unreasonable constraints” on access to the evidence, which prevented them from seeing it as a viable project for the broadcaster’s top current affairs programme.

Another problem was timing. The BBC source said Cadwalladr had given Panorama “a few weeks” to verify the claims in the story – an investigation which they claimed would have normally taken several months. The BBC ultimately turned down the opportunity to work on Cadwalladr’s story.

Cadwalladr told BuzzFeed News the decision to try to take the story to Panorama was Christopher Wylie’s: “When Panorama dropped both proposed programmes, (Wylie) chose to return to Channel 4. I supported his decision both times.”

Defending the decision months later – in a statement responding to Cadwalladr’s Observer colleague Nick Cohen who’d criticised Panorama for not taking it up – the BBC said Panorama had “limitations” placed on them, with not all the evidence made available to the programme.

James Stephenson, from BBC News and Current Affairs, said the corporation had been keen to work with Cadwalladr but had only come to them at a late stage.

He said: “Panorama asked for access to all the evidence, but that was not forthcoming. Limitations were placed on the BBC’s own investigation of the allegations and constraints on who we could approach. In short, we did not have the scope to make a programme which met our standards of robust independent investigation in the time available.”