Locking blade is not metioned specifically in the legislation.
No, but ‘fixed blade’ is, and there’s been a test case where a lock knife is classified as a fixed blade for legislation purposes. So yes, a locking knife is illegal to carry without good reason, even if it’s got a less than 3″ blade.
If challenged, it’d be down to you to demonstrate that “I need it to fix my bike” is good enough reason. Why, specifically, do you need a locking knife rather than a regular one?
In practical terms, police are trained to apply a degree of common sense and should be able to tell the difference between a bike maintenance tool zipped into a bag when cycling, and a lad in the pub with a bag of class As in one pocket and a 6″ lock knife in the other, so it’s unlikely you’ll get done for it. However, it’s a risk as you’re relying on the whim of a copper who might just be having a bad day.