In an updated travel advice, the Foreign Office said, "Further terrorist attacks in Tunisia, including in tourist resorts, are possible, including by individuals who are unknown to the authorities and whose actions are inspired by terrorist groups via social media."
Asking those who remained in Tunisia to be vigilant, it said, "You should be especially vigilant at this time and follow the advice of Tunisian security authorities and your tour operator."
Another 39 people were injured, including 25 Britons, in the attack.
Meanwhile, UK Home Secretary Theresa May, who chaired a meeting of the UK Government's emergency Cobra committee today, said that she has seen no evidence so far that the beach resort was targeted specifically because it is popular with British tourists, the BBC reported.
She, however, warned, that the risk to Britain had become "more diverse" in recent years - including not just the risk of groups plotting over time to strike in the country but also that of spontaneous attacks by a "lone wolf".