In the UK, all online brokers are overseen by the very experienced Financial Conduct Authority (FCA). FCA used to be under the jurisdiction of the EU's regulator ESMA, but after Brexit this has now changed. Still, however, FCA limits leverage to just 1:30 on major FX pairs for all non-professional traders in the UK.
With these strict regulations in place, we can hardly speak of any high leverage forex brokers in the UK anymore, as they all now only allow quite low leverage. What UK-based traders looking for more leverage can do, however, is to consider signing up with a broker that operates not only in the UK, but also for example in New Zealand or in a lightly regulated offshore jurisdiction.