BBC editors have been reprimanded and told that they must reveal the political backgrounds of contributors.

The landmark ruling comes after the broadcaster’s executive complaints unit upheld a viewer’s objection to a report failing to make clear the party allegiance of a businessman whose views were aired on the 6pm and 10pm BBC News bulletins.

In a piece on April 11 asking people in Merseyside for their reaction to Theresa May extending the Brexit deadline, the businessman spoke in favour of her position.

However, it was not made clear that the individual was an active Tory member and had stood as a parliamentary and mayoral candidate for the party.

The BBC’s executive complaints unit said: “As it could have affected viewers’ assessment of what he said, information about the businessman’s political affiliation should have been given.

“The editorial team has been advised that the political background of contributors should be provided when the subject matter is such that the audience needs to be able to calibrate the views expressed.”

SNP depute leader Keith Brown called for the same standards to be applied to the BBC’s Question Time.

In a broadcast of the show from Elgin last month, Mary Scanlon was allowed to speak for almost a minute from the audience.

At no point did the BBC inform viewers that Scanlon had been a Conservative MSP for 17 years.

Moray Conservative councillors Frank Brown and Claire Feaver and treasurer Jane Lax were also seen in the audience during the programme

Brown said: “This is a significant finding. It sets a precedent for far greater transparency for all BBC News and current affairs output.

“We’ve been warning the BBC for months that their vetting procedures are inadequate.

“It is fundamentally dishonest for the BBC to deceive viewers over who is asking the questions and stating opinions.

“Following Question Time last month in Elgin we asked BBC bosses to explain how a former Conservative MSP of 17 years could be allowed to contribute from the audience as ‘a member of the public’

“They have so far failed to give an adequate response to this.

“They may continue to try to wriggle out of accepting culpability but they’d do well to hold their hands up and admit they handled this badly before we go to regulator.

“Our concern is that viewers will lose trust in the BBC if this deception continues.

“BBC bosses need to get this sorted – they need to be more transparent, not defensive and refuse to admit mistakes.”

The BBC has maintained there is no relation between questions asked by audience members on a debate programme and its news output.

Asked for comment on the findings and Brown’s remarks, a BBC spokesperson simply said: “We’ve noted the finding by the Executive Complaints Unit.”

It comes after the BBC’s Tory debate show, Our Next Prime Minister, faced criticism over its vetting process.

Two people who asked the candidates a question have since been suspended from their jobs over old comments found on their social media accounts.