The agency now has just nine staff working in public affairs, compared with 20 in late 2008. A number of consultants have quit in recent weeks, while others have stopped working with public affairs clients.
Despite declining numbers, H&K CEO Richard Millar insisted: 'Our public affairs team continues to be among the best in the industry.'
H&K recently stopped working for London City Airport, London Chamber of Commerce and Toyota. The three firms are understood to be scaling back their use of external public affairs support, rather than turning to new agencies.
Earlier this year, H&K lost a key account with Kingfisher, Europe's biggest home improvement retail group, with the business moving to TLG.
Staff understood to have recently left the agency include consultants Alison Cairns, Sara Price and Wendy Blair. The trio's next moves were unknown as PRWeek went to press.
In the past 12 months, the agency's public affairs team has also been hit by the loss of managing partner Oliver Dowden, now at Conservative Central Office, and consultant Sophie Hudson, now working for former client Toyota.
The Association of Professional Political Consultants register sheds further light on the state of the agency's public affairs practice. The register shows that H&K had 30 public affairs clients and 20 public affairs staff in late 2008. On 31 August 2009, the agency had listed 24 clients and 13 staff.
This week, H&K confirmed the number of consultants in the public affairs team had fallen further since its last entry, putting the figure at nine.
However, Millar insisted the team was in good shape, pointing to a number of recent account wins under public affairs MD Paul Sinclair.
Millar said: 'Since joining from Downing Street last year, Paul has restructured and refocused the team and it is delivering some outstanding results for clients. It has added several new clients to the roster including Visa, Intercontinental Hotels Group, Statoil, Renault and Edwards Lifesciences.'