It’s not really legal in the UK. It’s unenforceable on claims under 5k and for claims over 5k the courts will make a case by case decision if arbitration is appropriate.
However, lots of companies still add these bullshit clauses as a way to bully people out of seeing a lawyer.
For part of a previous job I had to meet a bunch of people from GCHQ regularly.
Most of them were super friendly, but very obviously out at extremes of the spectrum. They were the kinds of people that other mathematicians would notice as being a bit odd.