The ITV newsreader Alastair Stewart is stepping down from his presenting duties following “errors of judgment in [Alastair’s] use of social media”, ITN has said.

The presenter – who deleted his Twitter account before the announcement – said in a statement: “It was a misjudgment which I regret, but it’s been a privilege to bring the news to households throughout the UK for the past 40 years.”

In an internal email, ITN staff were told that the decision, also backed by ITV, followed behaviour that breached ITN’s editorial guidelines.

ITN declined to provide details of Stewart’s behaviour. But his departure comes three weeks after a public social media spat in which he sent a Shakespeare quote to a black Twitter user including the phrase “angry ape”.

The tweet, which included the term as part of a line from the Shakespeare play Measure for Measure, was sent during a disagreement with Martin Shapland, a policy manager at the Institution of Civil Engineers. After Stewart’s tweet, Shapland wrote: “Just an ITV newsreader referring to me as an ape with the cover of Shakespeare … Alistair is a disgrace.”

Stewart, 67, first joined ITN as an industrial correspondent in 1980, and became the main presenter on News at Ten nine years later. He has also worked as foreign correspondent for the broadcaster, anchoring ITV’s coverage of the first Gulf War from Saudi Arabia, and for a time hosted Channel 4 News.

He has acted as one of ITV’s flagship newsreaders for more than three decades, working and moderated the first ever TV political leaders’ debate between David Cameron, Gordon Brown and Nick Clegg during the 2010 election.

His extensive career at ITV makes him the longest-serving male newsreader on British television.

In 2005, the Royal Television Society named Stewart presenter of the year, and a year later, he was awarded an OBE for his services to charity and broadcasting. He is a patron of Naomi House and Jacksplace, which provides hospices for children and young adults, and Scope, which supports disabled people and their carers.

The email to ITN staff said that “in recent times he has been a part-time freelance presenter mainly on the lunchtime news and weekend programmes”.

The ITV News presenter Julie Etchingham tweeted: “So sad to learn this – we have worked on many big stories together & Al is a trusted friend and guide to many of us.”

Her colleague Mary Nightingale posted that she was “very sad” about Stewart’s departure, adding: “He was a good friend and mentor to me when I started at Carlton TV, and we worked together for more than 27 years. I will miss him.”

Duncan Golestani, a presenter on both BBC and ITV, described Stewart as “one of the kindest men in broadcasting”, whilst BBC radio three presenter, Katie Derham said she was “so very sorry” about the announcement, saying Stewart was “a very dear friend and colleague; enormous fun and extremely supportive, and unbelievably well informed”.

“He will be missed,” she added.

Michael Jermey, the director of news and current affairs at ITV, said: “Alastair has been a longstanding, familiar figure to viewers of ITV News, both reporting and presenting with distinction. We wish him the very best for the future.”

ITN’s chief executive, Anna Mallett, added: “We would like to recognise Alastair’s contribution as one of the UK’s foremost journalists and TV presenters and to thank him for his commitment to delivering high-quality broadcast news over many years.”

• This article was amended on 30 January 2020 to remove the reference to Alastair Stewart being a patron of Scope. He stepped down from the role in 2012.

