The AA said there had been a slackening in consumer spending which had caused advertising expenditure to decelerate over the last six months.
Advertising expenditure in the UK totalled £3.779 billion in the third quarter of this year.
After adjusting for inflation, the 0.1% increase represents a 2.3% decline in real terms.
However, total advertising expenditure has risen by 2.9% for the twelve-month period ending September 2005.
The Quarterly Survey of Advertising Expenditure, compiled by World Advertising Research Center (WARC), includes national and regional newspapers, consumer and business magazines, television, radio, outdoor, cinema, internet and direct mail.
In the third quarter of 2005 six of the ten media covered by the report registered year-on-year declines.
The best performers were outdoor, which posted a 4% increase, television, which showed a 3.3% increase, and the internet, for which only an estimate of a 50% increase was available. Actual results for the internet will not be available until spring.