Watchdog Ofcom has announced its first broadcasting standards investigation into the BBC after Lord Nigel Lawson contested evidence about climate change on Radio 4’s Today programme.

The former Chancellor of the Exchequer appeared on the programme on August 10, when he claimed that there had been “no increase in extreme weather events” and that “mean global temperature has slightly declined” in recent years.

The broadcaster has already upheld complaints it received about the interview and said it “should have challenged” the claims.

In a letter seen by the Guardian, the BBC’s executive complaints unit accepted the interview breached its guidelines on accuracy and impartiality.

The publication quoted the letter stating that Lord Lawson’s statements “were, at the least, contestable and should have been challenged”.

The Ofcom investigation follows an incident in 2014, when the BBC found the programme in breach for another interview with Lord Lawson about climate change.

A spokeswoman for the regulator said: “We are investigating whether this interview, which followed a similar interview in 2014, breached our rules on due accuracy and due impartiality.”