The findings, from the Marketing Agencies Association, coincide with the launch of the new Agency Remuneration Best Practice Guide from the trade bodies IPA, ISBA, MAA and PRCA.
The average hourly fee for MAA member agencies declined 18.4 per cent from £129.55 in 2002 to £105.68 in 2011, according to the trade body, which represents 80 digital, direct, experiential and integrated agencies.
Fees for creatives were hit hardest, with a 26.6 per cent decline, while fees for account handling dropped 12.6 per cent during the period. However, planning fees rose 8.9 per cent since 2010.
This statistic does not apply to members of other agency bodies, which have grouped together to issue the first best-practice guide on remuneration since 2005.
The guide offers a checklist of best practice and looks at the principal payment systems as agency remuneration models evolve to encompass project, consultancy and payment-by-results fees.
Debbie Morrison, the director of consultancy and best practice at ISBA, said: "Advertisers are constantly searching for remuneration nirvana and are always interested in what's new to experiment with and adapt for their own agency relationships."