It is my opinion that Brexit will have no impact on the regulation of the forex market, or any other financial market, in the U.K.
The U.K. is a member of The International Organization of Securities Commissions (IOSCO) and, as such, has entered into numerous Multilateral Memoranda of Understanding (MMoU’s) with that organization. In fact, the U.K. (along with the U.S. and other major players in world markets) is one of the heavy-weights in the IOSCO syndicate.
IOSCO is the vehicle by which the CFTC is securing its position as World Forex Police.
Brexit represents the divorce of the U.K. from the E.U. Brexit will not affect U.K. membership in IOSCO, and will not alter the U.K.'s obligations under IOSCO MMoU’s. We can expect the U.K.'s FSA to continue to work hand-in-glove with the CFTC before, during, and after Brexit.
For more on IOSCO, and Multilateral Memoranda of Understanding, see this post —
For more, refer to these IOSCO webpages –
Finally, for anyone who thinks WORLD FOREX POLICE is an exaggeration –