It's quite situational aswell. So if the police get called in because secca have caught you and you are causing lots of trouble and getting aggressive with them, then having a blade on you is gonna get you in a world of trouble. On the other hand if you are pleasant and it can be seen that you are being polite and have a good attitude then it will be way less of an issue.
I actually asked this question on the r/UKpolice subreddit a while back, and the generaly opinion that as long as you weren't caught on a dark street corner where there was recently trouble, and the tool itself is reasonably sensible justify, then your gonna be okay. ie small SAK multitool or a smaller leatherman ie easier to justify as its got a wide range of uses. However a dedicated folding blade like a Spyderco or Opinel is harder to justify as its got less general uses, even know they might still be 'legal carrys'.
To be honest its all a bit grey, but don't be a tit, have a good reason ready and you should be okay.