The new patients, aged between 15 and 20, were staying in quarantine hotels at Chek Lap Kok, Wong Chuk Hang and Shek Tong Tsui when they developed symptoms on Friday or Saturday.
The three were also found to carry the L452R mutated virus.
Hong Kong has implemented a ban on flights arriving from the UK since July 1, citing a rebound in coronavirus cases and the spread of the mutated variants there.
Meanwhile, the outbreak in Hong Kong has continued to stabilise, with officials reporting only one untraceable local case and two import-related infections over the past two weeks.
For the untraceable case which involves a cleaner of a quarantine hotel in Yau Ma Tei, health authorities say they have collected 44 environmental samples from the facility.
Two of the samples gathered from a bathroom sink in a room are said to have tested positive for the virus.
Experts have earlier criticised the way the hotel room – which was previously occupied by an infected Indonesian woman – had been disinfected, saying the cleaning time had been too short and that wrong disinfectants had been used.
So far, the city has recorded 11,942 Covid-19 infections.