Visitors are staying away from some of the UK’s biggest attractions after the recent terrorist attacks in London and Manchester, according to the company behind London Eye and Madame Tussauds.

Merlin Entertainments said demand for day trips fell among domestic tourists after the Westminster attack on 22 March, and deteriorated further after the subsequent attacks in Manchester and at London Bridge.

Europe’s biggest attractions group, which runs Sea Life centres, Alton Towers and Legoland resorts, said the attacks could have a knock-on effect on demand from foreign tourists in the coming months.

“The impact of recent terror attacks on our London attractions is unclear at this stage,” said Nick Varney, Merlin’s chief executive.

“What is clear, however, is that London has bounced back before and will do again. I have every confidence in the longer term resilience and growth trajectory of the market.”

Trading at Legoland was in line with expectations, Merlin said in a update for the year so far, but there was a drop in visitors to a number of its parks as people were apparently put off by the attacks and heightened security at venues. The update did not mention if there had been any impact from the temporary closure of water rides at Alton Towers, Thorpe Park and Legoland after an accident in May at a similar attraction at the Drayton Manor theme park, which is not part of the Merlin group.

Merlin shares were the biggest faller in the FTSE 100 in early trading on Tuesday, down 3.5%, although they later recovered slightly to 2.8% down.

Business at Merlin’s London attractions had improved in the early part of 2017, as foreign visitors took advantage of the weaker pound.

Laura Citron, the chief executive of London and Partners, the agency that runs visitlondon.com, said she was hopeful that tourists would continue to come to the capital.

“It’s impossible to predict what impact recent events may have on the tourism sector, but anecdotally we are not seeing a wave of cancellations. Londoners and visitors are resilient and we are confident that tourists will stand by the city,” she said.

On Tuesday, the riverside around the London Eye, which is just yards from Westminster Bridge, was busy with tourists and daytrippers nonetheless.

One domestic visitor, Stuart Brown, said: “We didn’t think twice. We don’t live that far away and had the week off so decided to come into London. We’re not worried at all. It is quieter than usual but we haven’t felt nervous. We’re just doing what we normally do.”

Laura Braun, a teacher from Cologne, Germany, who was travelling with 53 young people, said only one child had dropped out of the trip. The group was one of several school groups milling about the London Eye. “We felt we would come as this could happen anywhere. We are from a big city in Germany and it could happen there as well,” Braun said.

Peter and Christine Jacob. Photograph: Sarah Butler/The Guardian

“The attacks had no bearing on anything we are doing,” said Peter Jacob, visiting from Los Angeles as part of a cruise trip with his wife Christine. “Here it’s a safe city even with this little bit of nonsense. I try to be alert but we’ve been on Westminster Bridge, we’ve been to the theatre. It hasn’t put us off going anywhere.”

Lydia Cogger Photograph: Sarah Butler/The Guardian

Lydia Cogger, who runs the Golden Carousel ride near the London Eye, said business had been slower than normal: “It is always quiet just after the school holidays anyway. The busiest Saturday was the Saturday of the attack. People were cautious after the Manchester attack but by Saturday quite a few brought the kids out for the day. Since then trade has dropped. After the Paris attack things dropped off quite a bit, it took a week or so to come back.”

Overall, Merlin said, trading in the year so far had been “broadly in line with expectations”. The group is expanding internationally and Legoland Japan opened on 1 April. A Sea Life centre in Chongqing, China, is scheduled to open on 15 June and Little Big City is expected to open in Berlin in July.

Varney said: “Merlin has a diverse portfolio of global brands with more than 70% of 2016 profits from outside the UK, and this proportion will only grow over time as we continue to invest internationally. I remain confident in the company’s underlying growth prospects.”

The company will publish its results for the first half of this year on 4 August.