These (ridiculously stupid) blade laws aren't so cut and dry (no pun intended). There are exceptions made such as whether it is used as part of your trade.
I'd imagine a particularly bored jackboot with nothing better to do (and absolutely zero understanding of the law, like most of them) would try to have you prosecuted for carrying this on your keys. They'd try to argue that it belongs in your vehicle, then argue that it must be kept in the boot rather than the glovebox... because they lack the intelligence necessary to recognize that this tool is of no use to you in the boot of the very vehicle whose seatbelt prevents you from accessing it.
A sane prosecutor (a beat I've yet to meet) would laugh at this and not even bother pressing ahead with it.
The anti-knife laws actually render themselves unenforceable in any legitimate way by defining a knife as a "weapon", which it is not. A knife is a tool, and a weapon is anything used to inflict harm on others... ergo these knife laws are invalid. Last I looked, they haven't illegalized glass bottles despite the fact that they can instantly be turned into a sharp weapon. They haven't illegalized pens, despite the fact that you could very easily stab someone in the eye and kill them with one. Why? Because a pen is a tool... and so is a knife!
I think it's obvious at this point that I have zero respect for what are hilariously stupid laws.
Carry it... and if the fascists prosecute, drag it through the courts. Drag it through the press, and let everyone laugh at them. Then sue the lot of them for the inconvenience of it all. Seat belt cutters, after all, are not illegal!