The online casino Sky Vegas offered free “spins” to recovering addicts during the industry’s annual Safer Gambling Week, prompting concern that the messages could trigger relapses.

The UK’s Gambling Commission is investigating the incident, which has emerged in the same week that Sky Vegas’s parent company, Flutter, boasted of its improved safer gambling measures.

It comes as the UK government finalises proposals to reform the way the industry is regulated, which could include a crackdown on advertising and marketing.

The incident, for which Sky Betting and Gaming has apologised, meant people who had voluntarily barred themselves from playing slots and online games such as roulette received promotional emails.

One email, sent on Tuesday, carried the subject line: “Take a peek at what your mystery bonus is.” It read: “Here at Sky Vegas, we love the unexpected. That’s right. Simply opt in, spend £5 and claim your 100 free spins. The best part? Whatever you win is yours to keep – that’s the fun in fair!”

The promotional message featured graphics of slot machines and the slogan: “Entertainment like no other”.

The messages were sent to people who had opted out of receiving direct marketing. They also went to recovering gambling addicts who had signed up to “self-exclude” from online casinos and sports betting sites.

About 218,000 people have signed up with the industry-wide self-exclusion scheme, Gamstop, after a 25% surge during the Covid pandemic. Under the conditions of holding a licence of offering gambling products, operators must remove self-excluded people from any marketing communications.

Sky Betting and Gaming has breached these licence terms before. In 2018 it was fined £1m for the transgressions, including sending promotional material to 50,000 customers.

Flutter, which also owns Paddy Power and Betfair, said on Tuesday that its financial results had suffered because it had tightened safer gambling controls.

Recovering addicts said the messages, inviting them to gamble in order to receive bonuses, put them at risk of relapse.

Adam Peck, a playwright who lives in Bristol, received the message despite having signed up with Gamstop, and said he tried to bet as a result.

“I thought if I’m receiving promotional material then my self-exclusion might not be working. I tried to access my account and get my password reset,” he said.

“They shouldn’t be targeting anyone, let alone people who’ve told them they have got a problem with gambling and it could be triggering. That it’s happened during Safer Gambling Week is perverse.”

Another former gambler, who asked not to be named, received the email despite having opted out of direct marketing from Sky Vegas in 2018 and later having his account closed by the company, after he revealed he was struggling with addiction.

He said seeing the advert after almost three years in recovery had hit him hard mentally, adding: “I worry that it may have caused others to relapse back into gambling.”

The incident is acutely embarrassing for the industry because it comes during Safer Gambling Week, an annual initiative during which operators proclaim their attempts to protect addicts and vulnerable people.

The industry has also been at pains to point to improved ethics as the government prepares to publish proposed changes to how the industry is regulated.

The former Conservative leader Iain Duncan Smith said the “utterly shocking” incident showed the industry could not be trusted to improve safer gambling protections voluntarily.

“People who are trying to stop and make sure they don’t get sucked deeper into the vortex of debt are targeted. It’s outrageous. It shows us that self-regulation doesn’t work any longer for them.

“How often is this happening? Can they ensure it doesn’t happen again? This is very dangerous, we’re talking about people’s lives.”

Sky Betting and Gaming said: “We sincerely apologise to those who have mistakenly received Sky Vegas promotional communications and for the distress this may have caused some recipients.

“We are treating this matter extremely seriously and are thoroughly investigating how this happened as a matter of urgency.”

A Gambling Commission spokesperson said: “We’ve been made aware by members of the public that Sky Bet have sent promotional emails to self-excluded customers yesterday. We do not expect this of our operators and we will be looking into how this has happened.”