Tobacco companies have been accused of undermining plain packaging laws by introducing gimmicks that ensure their cigarettes stand out from rival products but do not breach regulations.

A report in the British Medical Journal’s BMJ Open publication found that global tobacco companies adopted subtle marketing techniques to replace traditional cigarette branding, which was banned in the UK in 2016.

One of the MPs who pioneered the legislation said ministers should consider tightening up the law to eliminate loopholes detailed in the report, written by academics at the University of Bath.

Researchers found that tobacco companies initially ramped up production before a one-year “sell-through” period, during which retailers were allowed to keep selling their remaining branded packs. This had the effect of keeping the older packs on sale for as as long as possible, maximising brand exposure in the run-up to May 2017, when they could no longer be sold.

In the meantime, they came up with innovative ways to make plain-packaged products distinctive. Philip Morris International redesigned its premium Marlboro range, adding bevelled edges and a new “pro-seal” closing mechanism to packets, the researchers found. This made packs “appear more premium and recognisable compared to other brands”, the researchers claimed.

The report also pointed to the terms introduced by tobacco companies to describe the filters on their cigarettes, such as “advanced” or “firm”.

The researchers said previous studies suggested that such differentiating features “perpetuate the perceptions that some tobacco brand variants are less harmful than others”.

“Given that the tobacco industry is attempting to circumvent standardised packaging legislation, other countries considering the policy should consider how to make regulations as comprehensive as possible to prevent the exploitation of continued marketing opportunities,” the report concluded.

Tobacco companies have also responded to a ban on taste descriptions, such as “menthol” or “smooth”, by replacing them with names based on colour. Researchers said that banning terms such as “smooth” and “light” was meant to dispel the myth that certain types of cigarette are less dangerous, but that by teaching customers colour codes linked to the old descriptions, “misperceptions are likely to endure”.

Another tactic used by the industry was to introduce flavour capsules previously reserved for the most expensive cigarettes into less costly products. The researchers said flavoured cigarettes were more likely to appeal to less regular smokers and young people.

The Labour MP Alex Cunningham, who was one of the key proponents of plain packaging laws, said: “No one should be surprised at the tobacco companies doing everything possible to protect their brands, undermine the law and grow their sales. Ministers must act to put an end to this practice.

“It is particularly worrying that they’re now turning to new flavoured products – similar to vaping – which the university’s research shows are proving to appeal more to non-smokers. This flies in the face of the legislation – [aimed at] a reduction of the number of smokers – and it is clear that we need to clamp down on tobacco companies who choose to circumvent the rules.”

The report’s lead author, Dr Karen Evans-Reeves, said the tobacco industry was “engaged in activities that undermined and continue to undermine the legislation”.

“Major tobacco companies will always try to find a way to market their products,” she said. “Based on the number of innovations we found in this study, we would encourage all governments considering implementing plain packaging legislation to consider how tobacco companies have adapted to the legislation in other countries and where possible, close any remaining loopholes.”

Philip Morris International, which owns Marlboro, did not respond to requests for comment. The Guardian previously revealed that the company produced Marlboro-branded metal tins in the run-up to the plain packaging legislation coming into force. The move was criticised as a ploy to prolong the visibility of Marlboro’s brand in the UK.