A gunman raided a beach hotel in Sousse on Friday, killing 38 people.
"All 30 British victims have been positively identified. We can say with a high degree of confidence that that is now the final death toll of British nationals killed in this incident," UK Foreign Secretary Philip Hammond said.
"We're repatriating the bodies of another nine who will return to the UK today. There will be two further repatriation flights tomorrow and Saturday," Hammond said.
Tunisia beefed up security amid investigations on whether the suspected gunman, Saif Al-Deen Al Rezgui, had accomplices in Friday's deadly shooting.
Seven Tunisians have been arrested, court spokesman Sofiene Selliti said.
Selliti said the suspect's phone was recovered from the sea near the beach and had "very important information." He did not provide details on what the information was.
Tunisia's Foreign Ministry said victims came from various nations, including Britain, Germany, Russia and Ireland. But Britain suffered the heaviest loss.
The gun rampage is the most significant attack against British citizens since the London transport bombings 10 years ago
As investigations continue, authorities said there is a possibility of a link to another Tunisian terrorist attack.
Al Rezgui, 24, trained with the people who carried out the attack on the Bardo Museum in Tunis
in March, Tunisian authorities said.
In an online audio statement, ISIS -- which has said it's behind the beach resort attack -- claimed responsibility for the Bardo Museum attack. CNN could not independently verify the legitimacy of the audio claim.
Police shot Al Rezgui dead near the beach Friday, and authorities have said he carried out the attack alone.
Another suspect being sought in the Sousse and the Bardo Museum attacks is Shams Eddin Sindy, according to the Interior Ministry's webpage.
Britain will mark a week from the date of the attack Friday with a minute's remembrance at noon across the UK and at British embassies worldwide.