[5] He was a Presiding Judge on the Midland Circuit from January 2010 to December 2013, later appointed as a Legal Member of the Special Immigration Appeals Commission in 2013.
Following a spell as Judge in Charge of the Commercial Court, he was appointed a Lord Justice of Appeal in December 2016[6] and sworn of the Privy Council.
[7][1][2] In 2020, Flaux delivered the Court of Appeal's judgement in Begum v Home Secretary, granting Shamima Begum judicial review of the Home Secretary's decisions to revoke her British citizenship and to refuse her leave to enter the UK from Syria, where she had joined the Islamic State.
[10] In December 2022, in a case brought by Alexander Darwall (owner of 4,000 acres (16 km2) of land in southern Dartmoor National Park), he controversially ruled that a previously assumed right to wild camp without landowners' permission was legally wrong and that permission was needed.
[11] This proved to be a flawed decision: it was overturned on appeal in July 2023 [12] and the appellate court judges' judgments made clear that they thought the initial ruling a peculiar one with Underhill LJ commenting that it is “a perfectly natural use of language to describe [camping] as a recreation, and also as occurring in the open air, notwithstanding that while the camper is actually in the tent the outside air will be to some extent excluded”.