Dr James Murphy, head of risk substantiation at BAT, said the company had to be sure that other tests weren’t just saying e-cigarette vapour had a reduced impact because it was lost in the air.
The latest tests used new methods to checked whether the data could stand up.
BAT used two different robots, one smoking traditional cigarettes and one smoking one of the company's Vype ePens to run its checks.
The results show, puff by puff, e-cigarettes deliver less nicotine despite contributing more mass to lung cells. This is because vapour is made of heavier, but arguably less harmful, materials like water and flavouring.
Public Health England, an executive body of the UK Department of Health, last year published a report saying experts currently estimate using e-cigarettes is around 95 per cent safer than smoking cigarettes, although more research is needed.
The Royal College of Physicians have also said e-cigarettes should be widely promoted as an alternative to cigarettes.