Portcullis has seen a number of staff leave and be replaced since January, with 17 working for the firm in January and 14 now, three of whom were hired during the summer.
Those who have left the company this year include the CEO, Stephen Day, for Burson-Marsteller, and Rebecca Lynch and Matt Shearman, both former senior account executives, who left in May for Hanover and Ogilvy respectively.
A source claimed Portcullis was considering a merger with Butler Kelly, adding: "It’s a shame that one of the last independent public affairs firms is facing these challenges. It remains unseen whether it will be able to weather the storm."
Portcullis denied that a merger with Butler Kelly was in the offing but admitted that the two businesses had been "sharing resources" for a fortnight.
Charles Cockburn, chairman of Portcullis, said: "Portcullis Public Affairs has welcomed Butler Kelly to 11 Haymarket in an office-sharing arrangement. It is not correct to describe this as a merger of the two businesses, more a sharing of resources. This move is an important step in creating a centre of excellence at our central London office."
Cockburn said that Portcullis had hired three senior staff members from the world of government that would "enhance" its offering to clients.
He added: "I expect Portcullis to continue as a business."