Stanbrook, 45, regarded as one of the UK's leading experts on European advertising regulation, will focus particularly on developing the company's business within marketing and media.
A senior AA executive for nine years, Stanbrook quit the lobbying organisation in October 2000 to become the managing director of DLA Upstream, a public affairs company created by the law firm DLA.
During his period at the AA, he founded the Food Advertising Unit to explain and justify the ad industry's case for advertising to children.
The initiative led to the Children's Programme, which draws attention to legislative threats to children's broadcast media across Europe.
The move renews Stanbrook's links with Lord Plumb of Coleshill, the PRM chairman. He was Plumb's speechwriter and press spokesman when the Tory peer was the president of the European Parliament in the late-80s.
PRM's clients include trade associations and a number of Third World governments.