LONDON — Lord Bell has resigned from Bell Pottinger, the iconic UK public relations firm that he founded 30 years ago.

The 74-year-old plans to set up a consulting business called Sans Frontieres, the same name as the Bell Pottinger geopolitical risk consultancy that handled sensitive government assignments for the likes of Bahrain, Belarus and Sri Lanka.

Bell has been a high-profile advocate for this kind of political work, despite the controversy it has attracted. It is a stance that has proven increasingly anachronistic at Bell Pottinger, as the firm has endeavoured to move towards a more modern corporate communications positioning under CEO James Henderson.

Henderson became CEO of Bell Pottinger in 2012, when the firm bought itself back from Chime Communications to become a privately-owned partnership. Lord Bell remained chairman, and is understood to retain a 7% ownership stake in the firm.

Bell initially rose to prominence after helping to found ad agency Saatchi & Saatchi in 1970, and serving as Margaret Thatcher's PR guru. In 2014, he wrote a memoir that focused on this period of his career. Always outspoken, the Tory peer has previously described the PR industry as a "lightning rod for mistrust."

Bell Pottinger reported 2015 fee income of $67m, consolidating its position as one of the UK's biggest PR firms. The chairman role has been assumed by non-executive director Mark Smith, who is also COO at Chime.

In a statement, Henderson said: "Tim has been the founder and driver of this business since he started it in 1987. We are grateful for all he has achieved for both the PR industry globally and in building Bell Pottinger into a household name."

"He does not intend to retire totally and next year will be setting up a strategic consultancy to be named Sans Frontières. He will always be the founder of this business and we will find ways of mutually working together with him in his new business where there are clients that need a combined expertise."