The study by new business research company Pearlfinders points to a dramatic decrease in the opportunities available for PR agencies from third sector clients.
The figures cover the year to date and come out amid fears the lobbying bill, if passed, could stifle campaign spending in the run-up to the general election despite reassurances by leader of the House of Commons Andrew Lansley to the contrary.
There was more encouraging news for agencies in the financial sector, where the proportion of PR budgets allocated to agencies by financial sector clients rose from 4.5 per cent to 7.7 per cent, and the food sector, where there was a rise from 10 per cent to 12.3 per cent.
Pearlfinders MD Anthony Cooper said: "While budgets for PR agencies in the third sector have been decreasing, there is a growing need for charity expertise by CSR teams in the FMCG-food and apparel sectors.
"Agencies looking to bolster their client list should notice this shift, considering how their experience is now appealing to brands seeking to embrace ethical and charitable messaging at the core of their brand identity."
Pearlfinders' research also covered the US and, for the first time, Asia. In the US the voluntary sector again took the biggest hit, dropping to 3.7 per cent from 6.3 per cent, while food rose from 7.3 per cent to 11.2 per cent.
In Asia PR agencies claimed 19.1 per cent of budgets in the travel/transport sector – around three times their share in both the UK and US.
Industry and manufacturing were also strong, with a 12.8 per cent share each, but in the voluntary sector it was just 0.7 per cent.
The research comes from Pearlfinders interviewing 6,000 PR budget holders across the UK, US and Asia.
International spending on external PR by sector
'% PR Agency Opportunities' describes the percentage of client budgets allocated to PR agencies