Scientists went under cover in bars and pubs across Scotland and found “potentially significant risks of Covid-19 transmission” last summer, despite government guidance and the efforts of premises owners.

They visited a sample of 29 premises for up to two hours while posing as customers. Their report notes that “in Scotland, bars are numerous (52 per 100,000 people)”.

It was a sober undertaking for the undercover researchers, dubbed “fieldworkers”, who were dispatched in pairs for up to two hours, equipped with a small budget for non-alcoholic drinks and a snack and a smartphone to type notes of their observations.

They concluded that drinkers broke social distancing rules partly because being drunk made it hard for them to judge what 2m was, or to hear each other if they were too far apart. It also made them need to go to the toilet more.

The University of Stirling research, published in the Journal of Studies on Alcohol and Drugs, is said to be the first in the world to examine the measures tackling coronavirus in licensed premises.

Business owners and representatives were interviewed before reopening to understand the challenges they faced.

A range of incidents with potential to increase transmission risk were observed in all but three venues in the research carried out between May and August as bars began to reopen to the public.

One bar worker reportedly told the “spies”: “I also think if we make it too restricted and so we don’t allow for freedom of movement […] there is a risk that that would cause damage and people would cause damage and people would say: ‘Oh, I can’t be bothered.’ […] There is a balance that has to be, kind of, be met. […] Hospitality is the name of the game, and, you know, we’ve got to make it hospitable and attractive to go into rather than being too […] structured and too rigid.”

Another explained: “As the drink gets flowing, people will start getting stroppy and are not going to – well, potentially, it is there for them not to take too kindly to being told to keep their distance.”

Incidents deemed to be of greater concern, due to the repeated or continuous nature of the potential risk and the number of customers or staff involved, were observed in 11 venues.

These included combinations of singing, shouting or playing music; mixing between groups; standing and moving around the bar without distancing; customers taking photographs with other people and staff; and shaking hands or embracing others who did not appear to be in the same household.

The report also points out: “Alcohol affects judgement and coordination, including the ability to judge distances, and reduces inhibitions. It impairs hearing, meaning people may have to lean in closer to hear or shout to be heard, and has diuretic effects.”

Fewer than half of the venues had at least a basic system to limit the number of people using the toilets and most had no measures to ensure physical distancing, with no cubicles or sinks taped off.

In the majority of premises, no staff intervention in incidents or attempts to enforce restrictions was observed.

In some cases, staff intervened in a light-hearted way but such interventions were reported by the researchers as largely ineffective.

And while most venues required customers to provide details for contact tracing, nine businesses observed did not, including one venue visited after it was made mandatory by the Scottish government in August.

Professor Niamh Fitzgerald, director of the university’s institute for social marketing and health, led the research which was funded by the Scottish government’s chief scientist office.

She said: “Our study makes a unique contribution by providing the first evidence, including direct observation data, of how premises operated in practice when allowed to reopen during the Covid-19 pandemic.

“Overall, our findings suggest grounds for uncertainty about the extent to which new rules can be consistently and effectively implemented in a sector where interaction between tables, households and strangers is the norm, and alcohol is routinely consumed.”

The paper, Managing Covid-19 Transmission Risks In Bars: An Interview And Observation Study, also involved Dr Isabelle Uny, Ashley Brown, Douglas Eadie, Dr Allison Ford, and Martine Stead at Stirling and Professor Jim Lewsey of the Institute of Health and Wellbeing at the University of Glasgow.

However, Stephen Montgomery, from the Scottish Hospitality Group (SHG), called the paper an “out-of-date witch hunt”.

He said: “The government has paid hundreds of thousands of pounds on a six-month old study based on a tiny number (0.17%) of Scotland’s bars and restaurants.

“In reality we are talking about just a handful of premises. From those 29 targeted, criticism is levelled at in their own words a ‘substantial minority of observed bars’.

“You don’t need to be a mathematician to work out that basing the closure of a £10.5bn industry on this sham of a report would be ludicrous.

“We know that hospitality isn’t a vector and there’s no evidence to support that it is. The SHG members alone, which employ over 6,000 people, have had only 32 positive cases of Covid-19 among staff since July.”