Jack Dorsey, the founder of Twitter, said entrepreneurs in Europe lack ambition compared to those in Silicon Valley, as his micro-blogging website announced plans to expand its advertising sales in 50 new countries by the end of the year.

Mr Dorsey, 34, who was in Cannes to receive the Media Person of the Year award at the annual Lions advertising festival, said of Europe: "There's a huge barrier to entry because there's not a large ambition to take risks. There's a fear of making mistakes in public."

In contrast, he said there was a mentality on the West Coast of America that "I'm going to start something and it may fail but I'll learn from it".

He went on: "Silicon Valley has always been a whirlpool of technology conversation. I do wish some of that energy and attitude would spread to other parts of the world. I haven't seen it in many other places."

He was speaking as Dick Costolo, chief executive of Twitter, announced plans to start selling "promoted tweets" and other paid-for services in 50 new countries.

Twitter has 140 million users, with 10 million in the UK, but has only four ad sales offices at present, including one in London, and has been slow to generate revenue.

Ajaz Ahmed, co-founder of the London digital agency AKQA, which sold a majority stake to WPP earlier this week in an estimated £350m deal, voiced similar fears to Mr Dorsey.

"There just aren't enough tech success stories in the UK," he said. "Where are the Twitters, the Googles and the Instagrams in the UK? Where are the UK success stories?

"I don't think the UK celebrates entrepreneurs enough. It should encourage more of a meritocracy. Unless it's sport, Britain tends to have an uneasy relationship with success."

The need for creative people to embrace risk in both business and art was echoed by the philosopher Alain de Botton, who was invited to speak by the ad agency Ogilvy & Mather at Cannes.

"You can guarantee safety in mediocrity," said Mr de Botton, who argued that people were generally more willing to take risks in the internet age.

"You've got to gamble over time."

Miles Young, global chief executive of Ogilvy & Mather, said being innovative was more important than ever.