With rumours of a possible further terrorist attack over the weekend and an increased police presence in many parts of London, some tourists in the UK are finding it difficult to feel safe.

In the West End on Saturday night, the mood was unusually subdued. Theatre-goers could walk down Haymarket without dodging elbows. Ticket vendors at popular venues, such as the Warner Village cinema and the Duke of York's Theatre, said they had noticed a slight drop in attendances. "It's been quite calm," said a popcorn vendor at the Warner Village.

"I'm more worried about a potential attack than a war," said Tania Braem, 35, a health insurance broker from Belgium who spent the weekend in London. "If the Americans retaliate, the chances of a terrorist attack will increase."

Some tourists believe London is just as obvious a target as New York. "In Japan, we were told London could be next but I could not cancel my trip," said Naomi Suzuki from Japan. "I am afraid just walking in the streets. There are so many tall, old and beautiful buildings that could be destroyed."

Other tourists were more concerned about being stranded in London than being hit by a bomb. "What really worries me is whether I can fly out next week," said Mary Wright, a retired teacher from South Carolina.

Many Londoners tried to keep their cool and act as if nothing had changed, but some admitted to being on the alert. "I have not changed any of my habits," said Leo Lawlor, 65, a catering manager for a law firm in London, in the foyer of the English National Opera, waiting to see La Boheme and enjoying a glass of wine.

"But I have this awful feeling I am going to wake up one morning and all hell will have broken loose. We are going to suffer one way or another."

In the north London suburbs the mood is calm, but Gary Croft, of local agents Angel Travel, said some clients had cancelled trips in the past week, particularly to Muslim countries.

Nicky and Emma Stellar were in the process of cancelling their family holiday to Florida next year.

Ms Stellar, who went to the US last year, said she couldn't face sitting on a plane for nine hours, "thinking about what could happen, wondering if we could get hijacked ...I keep seeing those pictures [of the tower blowing up] in my head". She added they would holiday in Europe from now on.

• The British Incoming Tour Operators Association has predicted a 20 per cent drop in visitors to Britain this year as a result of the international situation coupled with the recent foot-and-mouth outbreak.