The IPA and ISBA's research revealed that an astonishing percentage - between 22 per cent and 45 per cent - are only being given verbal briefs.
The two trade bodies used the findings to unveil plans for a new set of briefing guidelines, to be launched by May.
The research also showed that although 99 per cent of agencies and 98 per cent of clients agreed that a comprehensive verbal and written brief is essential to achieve the best results, 70 per cent of clients learn how to brief through trial and error and 72 per cent rely on advice and guidance from their peers, rather than ever receiving any formal training.
The pitfalls are obvious. With so many briefs being written by agencies, clients will inevitably not be getting the work they imagined they were going to get. This means wasted money for the client, wasted effort from the agency and, inevitably, strained relations.
Michael Finn, the chief executive of DFGW, warns: "If the agency does not interrogate, and extract as much information as possible from, the client, it can mean creative work is done perhaps two or three times, only to be paid for once."
However, Andrew McGuinness, TBWA/London's chief executive, doesn't think a written brief is essential. He argues: "A shared agenda and clarity of objective are necessary, whether this is achieved using a traditional written brief or by means of verbal agreement." He believes in the free flow of information that is more likely to accompany a verbal brief than a written one. He explains: "Verbal communication helps to bring the idea to life."
His reservations are echoed by Tim Delaney, the creative director and chairman of Leagas Delaney, who fears that a formatted brief can be too rigid, preventing an easy flow of creative ideas.
Nevertheless, Debbie Morrison, the director of membership for ISBA, says the guidelines are being drawn up because she has received numerous requests from clients for guidance. She says: "We aim to meet the demand and put an end to bad briefing practices. We want our members to be able to communicate successfully with each other. This is good for long-term relationships and, in turn, good for brands."
There's no doubt that the guidelines will help in some instances. Delaney points out that some clients require more hand-holding than others: "The Procter & Gambles and Unilevers of this world set the standard in briefing, while the newer telecoms and dotcom entrepreneurs, enthusiastic amateurs launching their own companies, have little understanding about how to brief."
This is unarguable. Forcing any client, but especially an inexperienced one, to think through and define exactly what he or she wants from the agency will lead to a healthier relationship.
The trouble is that these younger, more naive, clients often won't admit they need help. They are also keen to prove their ability to think outside of the box. Delaney warns: "As soon as you make something uniform, people will break out of it to be different."