Huntsworth CEO Lord Chadlington declined to comment on the deal, but the group released a statement confirming negotiations were taking place.
The deal falls in line with Chadlington's aim to build the group's global financial PR offering, following acquisitions last year of Harrison Cowley, Woodside Communications and Stephanie Churchill PR.
Thomson put its consulting arm up for sale this year to focus on its core financial data and information offerings (PRWeek, 15 March).
Industry sources suggest the group had been in talks with a number of potential buyers, including The Interpublic Group, in a bid to sell off its consulting arm.
Thomson's IR business has lost a number of key employees since the decision to sell, including former EMEA head of strategic consulting Angus Prentice, who joined Brunswick as a partner six months ago.