Is it illegal?

[Scythe13]

A locking blade of any length is illegal, unless explainable as a work requirement/tool. Builders, roofers, farmers, and the alike, are all able to explain the reason they are carrying the lockable blade.

I'd opt for not being caught or getting any police attention in the first place. But to be fair, that's not too hard to do.

But, under strict rule of law, to the letter, unless you can explain why it was on your person, in direct regard to being a requirement of your job, then yes it is illegal.