The scale of harm done by gambling in Britain could be as much as eight times higher than previously thought, according to the largest ever survey into the impact of the industry.

An estimated 2.5% of British adults have struggled with “problem gambling”, according to new research. This would equate to 1.3 million people, though its authors cautioned there was a risk that the data could be an overestimate.

The Gambling Survey for Great Britain (GSGB) used a sample of almost 10,000 people to look at the impact of the industry.

Previous surveys, which were conducted by phone, had put the figure as low as 0.3%. It was acknowledged at the time that the earlier methodology meant this was likely to be an underestimate.

The latest research found that, among those who gambled in the last year, more than one in 40 experienced a severe harm to their life, such as a relationship breakdown, turning to crime to finance gambling or losing a home. Among men and young people, the rates were even higher. More than one in 20 of those aged 18-34 who gambled in the last 12 months reported a severe impact on their life.

Among men who gambled in the last year, 1.9% experienced relationship breakdown, 1.9% lost something of significant financial value such as a home, business or car and 1.6% experienced violence or abuse.

More than one in 10 of those who responded to the survey said they had considered taking their own lives and, of these, 4.9% said this was related to their gambling either a little or a lot.

Charles Ritchie, from the charity Gambling with Lives which supports families bereaved by gambling-related suicide, said: “These figures show what many of us already knew, that the harms caused by gambling have been massively underestimated, with millions of people in the UK affected. The number of people that have considered or attempted to take their own lives confirms the appalling scale of suicides happening now.”

Ritchie, who set up the charity with his partner Liz after their son Jack killed himself at the age of 24 after becoming addicted to gambling in sixth form, said: “Now legislation needs to catch up with this reality. The new government must immediately bring in a statutory levy on gambling industry profits to pay for vital prevention and treatment, and take measures to restrict gambling advertising.”

The new data is based on households being sent a letter inviting up to two adults to take part in the survey online. Because of the stigma attached to gambling it is thought that people were more likely to disclose problems using this method. It will be published annually so that trends can be tracked over time.

Produced by the National Centre for Social Research and the University of Glasgow, the latest survey has been independently reviewed and endorsed by a London School of Economics professor as being “exemplary in all respects”.

The figures suggest that the use of slot machines and online slots are more likely to lead to people struggling with problem gambling.

Problem gambling scores are calculated based on the answers to nine questions, such as whether someone bet more than they could afford to lose and whether it caused them health or financial problems. A score of eight or more signals that someone is experiencing problem gambling.

The proportion of participants with a Problem Gambling Severity Index score of eight or more was over nine times higher for those who had taken part in betting on non-sports events in person – such as slot machines – compared with all those who had gambled in the past 12 months. For those gambling on online slots, the rate was six times higher.

Tim Miller, the executive director of research and policy at the Gambling Commission, said: “One of our aims as a regulator is to ensure we gather the best possible evidence on gambling – and today’s publication is the next significant step forward in our journey on creating a robust source of evidence for gambling in Great Britain.

“Data in this report represents the first year of a new baseline, against which future changes can be compared and as such will prove invaluable in deepening further our understanding of gambling across the country.”

A spokesperson for the Betting and Gaming Council (BGC) seized on the Gambling Commission’s caveats about the potential for overestimating the data with the new methodology. They pointed to guidance from the Gambling Commission that it could not be used to “gross up problem gambling prevalence to the whole population”.

The BGC said: “Our members are concerned these findings may be unreliable because there is a significant risk GSGB overstates gambling participation and gambling related harm … The BGC and our members are committed to raising standards and we welcome any robust study that accurately gauges betting and gaming participation and problem gambling prevalence.”

Will Prochaska, from the Coalition Against Gambling Ads, said: “This new data, even with the caveats that the industry have pressured the Gambling Commission into making, is a source of national shame.

“The government must now treat gambling as one of the greatest threats to public health in society. Anything that liberalises or enables the gambling industry further will be a dereliction of the government’s duty to protect its citizens. The Culture Secretary should take urgent action to restrict gambling advertising and to put limits on the most harmful gambling products.”

• In the UK, Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international suicide helplines can be found at www.befrienders.org.