The attack in the resort of Sousse on June 26 killed 38 people, the majority of them British tourists.
In the Bardo attack, 22 people -- also mostly foreign tourists -- were killed.
Tunisian authorities have so far arrested around 150 people, of whom 15 have been charged with terrorist-related offenses, said Cmdr. Richard Walton, head of the Met's Counter Terrorism Command.
"While I cannot go into further details regarding this live investigation, I can confirm that a team of officers, led by a senior detective from the Met's Counter Terrorism Command, are working closely with the Tunisian authorities on both investigations and we have advised the coroner of the connection between the two," he said.
Tunisian authorities have previously named Saif Al-Deen Al Rezgui, who was shot dead nearby, as the sole gunman in the Sousse attack.
They say Al Rezgui, 24, trained with the people who carried out the attack on the Bardo Museum.
The Met Police said in a statement that a purported second gunman wearing red shorts -- referred to by some witnesses and reported on in the media -- is believed at this stage to be "a member of beach security who attempted to stop the attacker."
It added, "The investigators retain an open mind on this issue and will continue to follow up leads to clarify how many gunmen and weapons were used."
Since the Sousse attack, UK officers have taken more than 450 statements from witnesses and are examining more than 370 photographic and video files taken by witnesses on mobile devices, the Met Police said.
Tourism industry suffers
Specialist UK counter terrorism advisers have also traveled to Tunisia to help Tunisian authorities review security at popular tourist destinations and resorts, Walton said.
The UK Foreign Office last month advised all British nationals to leave Tunisia
, saying an additional terrorist attack was "highly likely."
That warning was just another blow to Tunisia's beleaguered tourism industry
-- already struggling to rebound after the upheavals of the 2011 Arab Spring
. Many Tunisians' jobs rely on tourism, which accounts for some 15% of the country's annual gross domestic product, according to a report
from the World Travel and Tourism Council.
Thirty of the 38 victims in the Sousse attack were British citizens, while those killed at the Bardo Museum included one British woman.