It has been against the law for children to use sunbeds in Scotland for the past five years, and in England and Wales since 2011. All sunbeds must be supervised by staff north of the Border.
However, the poll found 4.5 per cent of under-18s are still using the machines. Cancer Research UK said many children had side-stepped the rules by tanning at home.
The number of youngsters who use the machines has reduced since the law came into force - from 6.8 per cent in 2008/9 to 4.5 per cent, according to research which will be presented at Public Health England's (PHE) annual National Cancer Intelligence Network conference in Birmingham.
The survey, conducted by PHE and West of England University, also found half of those who had used a sunbed had burned at least once as a result. Every child who admitted using an unsupervised coin-operated bed on a regular basis said they had burned at least once.
The poll, funded by Cancer Research UK, was conducted on 3,000 11 to 17-year-olds from across England, Wales and Scotland. It also found four in ten of the youngsters said they never been given health advice on the potential harms of sunbeds.
Professor Julia Verne, lead author and strategic public health lead of PHE's National Cancer Intelligence Network, said: "Supervision needs to improve to adhere to the legislation which is designed to protect young people from the harms of UV damage."