The investigation into Cambridge Analytica and its parent company SCL Group that prompted raids of offices, and led to fines for Facebook (£500,000), Vote Leave (£40,000) and Leave.EU (£15,000) was possibly the largest by a data protection authority anywhere in the world. Ms Denham has admitted delays in another case had arisen because “her resources were diverted elsewhere (on the Cambridge Analytica matter, in particular)”.

The ICO investigation into Cambridge Analytica fuelled conspiracy theories that the UK had voted Brexit due to Russian interference and a campaign of lies channelled by Vote Leave through Facebook. But after more than three years Ms Denham closed her inquiry finding Facebook had wrongly shared data but no evidence of the wider conspiracy that its misuse influenced the EU referendum result.

In fact, in a letter to Julian Knight, the chairman of the Digital, Culture and Media and Sport Select Committee, sent in October 2020 and headed “ICO investigation into use of personal information and political influence,” Ms Denham concluded: “From my review of the materials recovered by the investigation I have found no further evidence to change my earlier view that SCL/CA were not involved in the EU referendum campaign in the UK – beyond some initial enquiries made by SCL/CA in relation to UKIP data in the early stages of the referendum process. This strand of work does not appear to have then been taken forward by SCL/CA.”

Mr Knight, a Conservative MP, said: “I was always fairly sceptical about the Cambridge Analytica investigation. I felt it was a means to fight the referendum by proxy all over again. I felt it was to give the unlikely grist to the mill to get a second referendum. I always thought Cambridge Analytica was just a collection of clowns. The whole thing [ICO investigation] was very, very over the top. There were some very serious issues about Facebook and the sharing of data and its lack of command of its data. But at the same time I don’t think it [the investigation] reflected that well on those who were involved in it.”

Ms Denham’s replacement, due to be announced imminently, suggested Mr Knight needed “to turn things around”, adding: “It does seem wrong that they have doubled staff but we still don’t see an awful lot of prosecutions. I wonder that the ICO should concentrate on the day job rather than chase the headlines.”

The frontrunner for the next Information Commissioner, incidentally, is John Edwards, New Zealand’s privacy commissioner, who once said of Facebook: “They are morally bankrupt pathological liars.” 

James Tumbridge, a leading data protection lawyer who has advised the Government, is critical of the ICO under Ms Denham’s tenure, concerned she has chased high-profile political stories like Cambridge Analytica mainly for publicity, and also gone after others based on media reports not based on complaints.

“The ICO is supposed to be the sword and shield to protect the British public from spammers, boiler room salesmen and nuisance callers. There should be more focus on protecting the public and on what is achieved.” said Mr Tumbridge, “I think Elizabeth Denham seems much more interested in big stories than the day-to-day problems the public experience. It’s a bit whack-a-mole going after nuisance callers and they are never going to be stopped, but there is a lot more she could be doing to make it harder for them to operate.”