On December 15, 2016, it was revealed that Tyler Bate and Trent Seven would be among of sixteen men competing in WWE's United Kingdom Championship Tournament on January 14 and 15, 2017 to crown the inaugural WWE United Kingdom Champion. Bate defeated Tucker in the first round to advance to the quarter-finals, before defeating Jordan Devlin to advance to the semi-finals. Seven would defeated H.C. Dyer in the first round and lose to Wolfgang in the quarterfinals, while Bate defeated Tucker in the first round, Jordan Devlin in the quarterfinals, Wolfgang in the semifinals, and Pete Dunne in the finals to win the tournament and become the inaugural champion. After the tournament, both Bate and Seven signed contracts with WWE. Bate would then compete on the NXT brand, where he defended his title; he eventually lost it to Dunne at NXT TakeOver: Chicago, in a match which later earn them the NXT Year-End Award for Match of the Year.
During day one of the second annual United Kingdom Championship Tournament event on June 18, British Strong Style (Bate, Seven, and Dunne) defeated The Undisputed Era (Adam Cole, Kyle O'Reilly and Roderick Strong) in a six-man tag team match. The next day, Moustache Mountain defeated O'Reilly and Strong to capture the NXT Tag Team Championship, but lost the titles back to O'Reilly and Strong on the July 11 episode of NXT. At NXT TakeOver: Brooklyn 4, they failed to regain the championships.
Both Bate and Seven were part of the original roster of the NXT UK brand upon the debut of the NXT UK show on October 17, 2018; they competed in a four-teams tournament to crown the inaugural NXT UK Tag Team Champions; they defeated Gallus (Mark Coffey and Wolfgang) in the first round on November 24 (aired January 2, 2019), and lost to James Drake and Zack Gibson (later known as Grizzled Young Veterans) in the finals at NXT UK TakeOver: Blackpool on January 12. After their loss, Bate and Seven kept on competing mostly as singles wrestler while continuing to team up occasionally; Bate notably unsuccessfully challenged Walter for the WWE United Kingdom Championship at NXT UK TakeOver: Cardiff. On the December 9, 2021 episode of NXT UK, Moustache Mountain defeated Pretty Deadly to win the NXT UK Tag Team Championship, making them the first team to win both the NXT and NXT UK Tag Team Championships. On the June 2, 2022 episode of NXT UK, they lost the tag titles to Ashton Smith and Oliver Carter in a triple threat match that also involved Die Familie (Teoman and Rohan Raja). On the June 16 episode of NXT UK, Seven turned on Bate by hitting him with a low blow from behind after making a fake retirement speech. Seven then slapped Bate across the face and declared that he never needed him, before finishing the attack with a Burning Hammer, leaving Bate lying in the middle of the ring, and disbanding Moustache Mountain.