On December 15, 2016, it was revealed that Seven would be one of sixteen men competing in a two night tournament to crown the first-ever WWE United Kingdom Champion on 14 and 15 January 2017. Prior to the tournament, Seven, along with Pete Dunne were mentioned among the favorites to win the tournament. In the first round, Seven defeated HC Dyer to advance to the quarter finals, where he was defeated by Wolfgang. Seven then signed a contract with WWE. On February 15, Seven made his debut in WWE's developmental territory NXT, unsuccessfully challenging Tyler Bate for the United Kingdom Championship. On November 11, Seven and Bate (going under the team name of Moustache Mountain) defeated the team of Pete Dunne and Mark Andrews. On December 6, Seven was defeated by Killian Dain in a #1 contender's qualifying match for the NXT Championship. At the United Kingdom Championship event, Seven formed British Strong Style with Bate and Dunne to defeat The Undisputed Era (Adam Cole, Kyle O'Reilly, and Roderick Strong) in a six-man tag team match on June 18. The following night, Mustache Mountain defeated O'Reilly and Strong to win the NXT Tag Team Championship, but lost the titles back to them two days at the June 21 NXT tapings (aired on July 11) after Bate threw in the towel due to Seven's injured knee being targeted.
After Seven's match with Zack Gibson on the November 14, 2019 episode of NXT UK, Gallus (Joe Coffey, Mark Coffey, and Wolfgang) would beat up Seven.
On the December 9, 2021 episode of NXT UK, Moustache Mountain defeated Pretty Deadly (Lewis Howley and Sam Stoker) to win the NXT UK Tag Team Championship. On the June 2, 2022 episode of NXT UK, Moustache Mountain lost the titles against Ashton Smith and Oliver Carter. On the June 16 episode of NXT UK, Seven attacked Bate, thus turning heel for the first time in his WWE career and disbanding Moustache Mountain. On August 18, 2022, Seven was released from his WWE contract.