Yep, but it actually breaks the UK system to have more than two parties so the existence of two parties there isn't actually a very good alternative. There's a lot of seats in the most recent election where the Conservative party lost only because the even further right wing Reform party took so many votes.

If I were to guess why third parties don't make much of a dint it'll be because successful movements gradually get incorporated into one party or the other via the primary system. Once a party has drained away the core appeal the third party or outside movement will flounder.