The company behind Alton Towers theme park, where 16 people were injured in a rollercoaster crash last month, has warned its annual profits are expected to be £26m lower than anticipated because fewer families have been arriving at turnstiles since the start of the peak summer holiday period.

Merlin Entertainments, which also runs Thorpe Park, Madame Tussauds and Legoland parks, said it would not meet City expectations for pre-tax profits of £275m this year, anticipating instead broadly the same outcome as last year, when it made £249m.

Within the group’s resort theme parks division, which includes Alton Towers, top-line operating profit is expected to be between £40m and £50m rather than in excess of £90m.

Merlin’s six resort theme parks generate 27% of revenues for the wider group and do much of their trade during a six-week summer spell after the schools break up.

Merlin has responded to fears of a repeat accident by emphasising its commitment to safety and by investing in promotional offers through the peak season. The company said last month that it accepted “full responsibility” for the incident. “Action is being taken to rebuild momentum and re-engage with our customers,” said Merlin on Monday.

Promotions include vouchers on the back of Kellogg’s cereal packs offering up to £49 of savings on a two-for-one Alton Towers ticket offer. Merlin described visitor numbers at the Staffordshire site as “significantly reduced”, adding that volumes had also fallen at other UK theme parks since the accident.

In April the group had opened its Enchanted Village accommodation facilities at Alton Towers, comprising 120 lodge houses and five tree houses, hoping to boost visitor numbers, attracting people from further afield and for longer stays.

Chief executive Nick Varney said a resumption in promotional activities had not been “moving the dial” as hoped.

Asked if Alton Towers might have to consider closing its doors, he said: “I don’t think there is any danger of that whatsoever … At the end of the day we have had one accident in the history of this company. I think, hopefully, people believe we have been responsible in the way we have acted.

“In 12 to 18 months’ time I believe Alton Towers will be back to where it was.”

He offered no update on the future of the Smiler rollercoaster. In June the group said it would remain closed for the foreseeable future, as would Saw, a similar ride at Thorpe Park. Saw, however, has since reopened.

Shares in Merlin lost 8% of their value in early trading on Monday, but recovered half of that fall to close down 4.3% at 405p. The profit warning came just three days before Merlin was due to publish its half-year results.

Headline figures from Thursday’s announcement were released on Monday to reassure investors that progress in the wider Merlin group remained on track. Comparable revenues were up 2.8% to £544m for the first half of 2015, with top line operating profit rising from £120m to £123m. Visitor numbers were up from 27.5 million to 27.7 million.

Varney again said Merlin was “deeply sorry” over the crash, which he described as a devastating event, and would continue to do what it could to support those who were injured and their families.

“We have committed to support those injured as best we can and implemented additional safety protocols to be sure that a similar accident will never happen again,” the company said. Two of the crash victims each had a leg amputated following the accident.

Varney said shutting down the park and suspending rides at other sites in the immediate aftermath of the accident had been “the right course of action reflecting the seriousness of the incident”. New safety procedures had been implemented where necessary.