Allchurch had been MD of the Buckinghamshire firm since the start of 2014, when she moved from Diageo. Another former Diageo comms leader was her deputy MD at Cirkle for just over a year.
Since she left the firm earlier in the summer, its chair and founder Caroline Kinsey has stepped back into day-to-day operations and is looking for a new MD. Kinsey said: "We have already met with a few strong candidates and are impressed with the talent in our industry.
"As an agile, entrepreneurial business, we are also delighted to announce that we have just opened a second office in the WeWork offices in Paddington. We believe this will be an excellent platform for further growth."
Kinsey, who set the firm up in 1998, is the sole owner of the firm. It has established itself as of the UK's largest wholly independent consumer PR agencies, with fee income just shy of £4m and a ranking of 77th in the 2017 PRWeek UK Top 150. Wins including a brief for supermarket Morrisons helped it to six per cent growth last year.
Allchurch said: "After three and a half super successful years at Cirkle, now is the time for me to move onto the next chapter in my career. I thoroughly enjoyed my years at Cirkle, growing the team and winning some incredible clients and accolades. I will always be proud of what I achieved as MD of Cirkle and I wish the agency all the best in the future."
PRWeek has also learned that Jonathan Smith, who joined the agency in December 2016, has departed. Smith, who was the director of Cirkle's trade division, left a short time before the departure of Allchurch.