A regional publisher’s investigation has revealed dozens of local political adverts targeting Facebook users have broken the social media website’s rules.

The probe by JPIMedia’s data unit found 40 targeted Facebook adverts placed on behalf of sitting MPs broke the site’s rules by failing to say who paid for them.

In the wake of the Cambridge Analytica scandal, the unit decided to look into the “as-yet-untold” local stories around political advertising on social media.

The investigation resulted in stories for 20 of the company’s titles – including some of its biggest daily newspapers.

Open data published by Facebook reveals thousands of adverts are being placed at a local level by MPs, councillors and other elected officials as well as local authorities.

The investigation identified around 300 ads on the pages of local politicians and councils which were run without declaring who had paid for them – including 40 placed on behalf of sitting MPs.

There is no suggestion that any of the adverts had been deliberate attempts to deceive constituents, but many had already been viewed thousands of times before they were all found and removed by Facebook.

Claire Wilde, pictured, JPIMedia’s news editor for data and investigations, said: “Facebook has now made a wealth of information openly available about who is placing political ads, as well as who is being targeted by them.

“It is important that we as journalists examine this and reporter Aimee Stanton has done a great job in finding countless stories of huge local interest.”

The JPIMedia titles to have published stories based on the findings are the Banbury Guardian, Bedford Times & Citizen, Blackpool daily The Gazette, Derbyshire Times, Doncaster Free Press, Edinburgh Evening News, Fleetwood Weekly News, Halifax Courier. the i, Lancashire Post, Lytham St Annes Express, Milton Keynes Citizen, Northampton Chronicle & Echo, Northamptonshire Telegraph, Pontefract & Castleford Express, Sheffield daily The Star, The Scotsman, Wigan Post, Yorkshire Evening Post, Yorkshire Post.

A spokesperson for Facebook said: “Our industry-leading tools are making it easier to see all political ads on our platforms, and archives them for seven years in Facebook’s Ad Library.”