Patent notification for CSP 2.0 usage

Hello,

I'm not sure where to ask about this, but as it's part of the w3 CSP specification, someone here may be able to provide some input.

I am in the UK and have received a recorded letter telling me that the nonce feature of CSP2.0 is covered by a prior art patent (UK & US). The letter continues to state that "Licensing applies to any organisation making use of their software or the intellectual property pertaining to their patent"

Obviously this feature is a documented part of the CSP specification which is widely used, and honestly I'm a bit surprised to get a demand like this for something that is part of an open internet standard.

I have a good mind to argue back that the actual implementation of this feature is in the browser and therefore he should be chasing Google/Microsoft etc, in which case I doubt he'd get very far, but IANAL and have no idea how it is determined who is infringing/liable. Effectively we've been forced to just stop using this feature as my superiors are not happy about getting license/patent requests for something I've used in our website (even if it is simply a HTTP header).

This person seems to have simply crawled our website and found a nonce in the CSP header so I would be surprised if we're the only business that have received this.
Any advice on this or direction on where I can ask to get an informative response would be appreciated.

Regards,
Matt Churchyard