This does present a problem in that a folding knife without a lock is substantially weaker but thankfully companies like Spyderco and SOG among others have released new ‘slipt joint’ knives which don’t lock but rely on a ball bearing mechanism to apply tension to the joint and keep it open. Because they are not locking they are still legal and a vast improvement over more traditional non locking knives like swiss army knives even if they don’t stand up to locking blades.
In my opinion the Spydercos are the best as they offer a range of blade styles as well as blade material (from cheaper metals all the way up to s30-v) and handle materials. I hope this helps anyone looking for a UK legal carry knife