There is something wrong with British culture that prevents one of Europe's biggest startups from flourishing here

BlaBlaCar, the $1.5 billion French ride-sharing app that lets people split the cost of fuel on journeys between cities, is one of the most exciting tech startups in Europe. It is growing like crazy on the continent and currently has 40 million members doing 4 million journeys each month.

But it is struggling to go mainstream in Britain, according to CEO Nicolas Brusson.

"Britain is very slow for us," Brusson told Business Insider at Web Summit in Lisbon. "Something is puzzling here." The company has "defocused" its efforts in the UK although the app and its service remains available for anyone who wants it.

On paper, Britain is perfect BlaBlaCar territory. Petrol is expensive. The trains are expensive, crowded, and service is often patchy. The roads are good. And millions of people need to make routine journeys between the major cities.

But for some reason, British people remain suspicious of the idea of sharing a long car journey with a stranger. It is, Brusson speculates, perhaps an extension of the famous British distaste for talking to strangers on public transport.

When BlaBlaCar took off in France, people said "it's a French thing, it's a socialist thing," and that is why sharing a car and the cost of a journey felt natural. When it took off in Spain, people said, "it's a Southern European thing."

"We become this trust broker [between strangers] in a peer-to-peer community, that's where we create value," Brusson says.

Not in Britain. A review of UK Facebook comments about BlaBlaCar found fear of legal issues, trust and issues to do with strangers were posted 10 to 20 times more frequently than in other countries - suggesting a deeper level of anxiety about car-sharing in the UK than elsewhere. This, after all, is the land that thoroughly rejected the "Tube chat" badges that encouraged people on the London Underground to talk to each other.

BlaBlaCar is doing well elsewhere, though. It now has 550 employees in 22 countries. The company has taken $300 million in investment funding and was worth $1.5 billion at the last valuation, Brusson says. He declined to give us a revenue number but did say that the cut per ride average is €15-20. (The US dollar and the euro are close to parity, currently.) In newer countries, BlaBlaCar takes no cut.

We can estimate that:

• 4 million journeys per month
• multiplied by €15 each
• = €60 million per month
• = €720 million annually, assuming all journeys are monetised (which they are not).

That's up from last year, when Brusson told Business Insider that BlaBlaCar had 20 million members, and 10 million people traveling every quarter. We estimated revenues at €96 million annually at that time.