Susan Goss-Clements of Ventura, which commissioned an NOP survey of different countries' approach to complaining, says Britons are changing.
"From five years ago, 64% of us say we complain more. So we are no longer turning the other cheek, we're complaining a lot more.
"And we're more prepared to go elsewhere if we get bad service."
More than half the British people surveyed said they had complained to an organisation about poor service.
This compares with 43% of Germans, 40% of French and 26% of Italians.
But UK firms were rated worst for customer service and are warned they must improve to compete with their international rivals.
Solicitors were judged to provided the poorest service by those surveyed, while telecommunications was pronounced the most improved service.
Companies in the United States give the best service to their customers, according to Ventura's survey.
Ms Goss-Clements said UK firms needed to learn lessons from their overseas counterparts quickly.
"The weakness of customer service among UK business may not only hinder their efforts to expand in Europe, but also leave them open to European rivals which can poach domestic customers by claiming a superior service," she said.