Until previous year it had advised against all but essential travel to the country.
This is because their governments did not recommend that their citizens should not visit Tunisia. Another flight to Enfidha will depart from Gatwick airport on Wednesday.
38 tourists, including 30 Britons, were killed in June 2015 when gunman Seifeddine Rezgui opened fire at the five-star Riu Imperial Marhaba Hotel. The attack caused the UK Foreign Office to advise against travelling to Tunisia unless it was essential, though it has recently downgraded its warning.
Terror group Isis claimed responsibility for the shooting.
Capacity in Spain has increased in recent years as operators have moved from destinations in the Middle East and North Africa in the wake of attacks on tourists.More news: Kim Kardashian West exhibits her tiniest waist till now at 24 Inches
Before the massacre, Tunisia was one of the most popular holiday destinations for British people.
Inveryes wrote: 'Why wouldn't you want to lie on a beach whilst heavily armed police on quad bikes cruise up and down.
Tourism provides much needed jobs and foreign currency in Tunisia, but it has struggled since the attack in the resort of Sousse killed 39 holidaymakers and an earlier one at the Bardo National Museum in Tunis left 21 dead.
The return of Thomas Cook, which is operating three weekly flights to Enfidha-Hammamet, marks a significant moment for Tunisian tourism as January figures show considerable improvement with respect to the same month a year ago.
"It's great news that Thomas Cook are welcoming visitors back to Tunisia", said Samir Ben Haj Fraj, 19, who was a passenger on the flight.
TUI said its decision to resume holidays to Tunisia was due to returning appetite.