I've come across this 'solicitors' firm before, a quick search of their name + 'scam' will give you an indication of their integrity.
I would be very surprised if Chubby Gorilla are behind this mailing, they may not even be aware of it.
The Registered mark for 'Chubby' is for the US only (unless I am misinformed)
The last thing I would ever do is contact them though, once you do that, they know there is someone (a business) ripe for making a demand to. It's basically a form of 'legal' extortion, although the legality is very questionable.
If you're genuinely concerned, take legal advice, but I wouldn't necessarily take it to heart that you have been targeted, it's little more than phishing using snail mail.