By Lisa Mitchell BBC News Online in Dover

Drivers had more to be worried about than a rough crossing as they waited for ferries at Dover on Tuesday morning.

As slate grey waves crashed against the harbour wall, they listened nervously to news reports that a terror threat for ferries crossing the North Sea to the UK had been intercepted.

The specific warning was about a lorry loaded with explosives could be on its way to a UK ferry port.

It was difficult for them not to eye each lorry trundling onto the roll-on/roll-off ferry with suspicion.

Several young Australians travelling to France in a camper van loaded with sleeping bags were shaken by the early morning reports.

Now it feels as if you can't even trust your best friend - they might be a terrorist

Mary Arnold, ferry passenger

Memories of the Bali bombing, in which more than 100 Australians died, were fresh in their minds so it was difficult to be blas� about the threat.

Jesse White, a 22-year-old painter from Sydney, said: "It's pretty scary. Bali showed no-one is safe.

"We have all been to Bali and even drunk in the club that was blown up - it was a reality check."

Aussie electrician Sean Coutts, 23, said: "We used to always think things like that wouldn't happen to us, but after Bali we're scared.

"But we thought we would be safe in Britain."

Lack of trust

Older travellers appeared more willing to take the latest threat in their stride.

James Arnold, 71, from Broadstairs, Kent, said he agreed with the prime minister when he told people to be vigilant but to go about their daily business.

"You can't let them win," said the defiant pensioner, who was off on a cross-Channel shopping trip with his wife Mary.

Plenty of asylum seekers get on lorries and get through the port, so why shouldn't a bomb?

Phil Sinden, truckers' cafe owner

Mrs Arnold, 72, was not so confident.

"It's so different from World War II. Then you knew who your enemies were.

"Now it feels as if you can't even trust your best friend - they might be a terrorist.

"The Germans wouldn't have targeted a ferry full of families going on holiday."

Denis Read, 73, from Ramsgate, Kent, said: "You never know when they are going to strike - there are no rules.

"Everyone is on the front line."

Trade threat

There was a more visible police presence around the docks with vehicles not being allowed to stop anywhere unusual even for a moment.

Lorries were being stopped and searched by customs officials.

Truckers tucking-in to fry-ups at Phil-U-Up, a roadside cafe just outside the port, said they had been told not to talk to the press about the threat.

Extra security checks are being carried out at Dover

But caf� owner Phil Sinden said they had been complaining about being delayed by the searches.

Mr Sinden said the threat was real and added: "Plenty of asylum seekers get on lorries and get through the port, so why shouldn't a bomb?

"I'm worried about business because people will be scared to travel.

"I'd seriously think about not going if it was me."

But back at the dockside the blitz spirit prevailed.

Robert Hammond, 59, from Deal in Kent, admitted he felt uneasy, but he would still be taking his day trips to Calais.

"You've got to get on with life haven't you?"