The increase in strikes could put off foreign firms from investing in Britain, the CBI's leader has claimed.

Digby Jones warned on Friday that the country's reputation for having a flexible workforce was being questioned by international firms following the series of high profile disputes over the past year.

Ahead of next week's CBI national conference, the director general said concerns about labour relations had been raised with him by officials at two automotive and construction companies during a visit to the United States.

Picket lines have been making headlines this year with two high profile industrial actions involving post office workers and fire fighters.

"Our members are worried about growing militancy among trade unionists. It puts up a very bad sign for UK plc abroad," said Jones.

"When overseas investors see the militancy among trade unionists it will have an effect."

He went on to claim that problems with the crumbling transport network and taxation were hitting Britain's position as Europe's leader for inward investment.

On transport issues, Jones argued that progress was "painfully slow".

He said Heathrow must get another runway in order keep its position as Europe's main airport.

"Other nations are catching us up. At a macro economic level, the government has helped deliver low interest rates and low unemployment but, at a micro level, alarm bells are ringing about whether we are as competitive as we used to be," Jones said.

"Some of that is down to the government. Some is down to trade unions or the UK's planning regime, which is the best friend countries like France have got."

But Jones also accepted that bosses were part of the problem.

"Some is down to business itself because we don't invest enough and train people as well as in other countries," he said.

The prime minister, the chancellor, the trade secretary and other senior ministers are expected to be among those joining the CBI conference in Birmingham next week.

Jones said contact with the government was at its highest-ever level - but he added that business had growing concerns about Europe.

"I wish Brussels would come up with ideas that would help the 12 million unemployed people in Europe find work," he said.