Hi thanks for the information, sorry for the short delay coming back to you, I was looking at the design right page, your page and their web pages.
It is a little strange that the alleged registered design owner is a company in Scotland and yet the mould company is in Norfolk. However, their method of contact is very aggressive and rather unprofessional. This is a civil dispute and therefore the police should not get involved.
I would write back to them and advise them that you considered their notice of a claim against you is as invalid as their claim of a registered design. Inform them that if they wish to proceed with any matter they should write to you in a formal and professional manner and at that point in time you will consider the matter further, however, from the information in your possession, you would be defending any claim of infringement on the basis that you consider that their "registered design" is invalid and defective.
One of the requirements for obtaining a registered design is that the design must be new. If you can find examples of similar designs that pre-date their registration you can inform them that their registered design does not fulfil this essential criteria and should be cancelled.
Having looked at their design, is not unique at all. Indeed, it clearly copied from a bar of chocolate design, also as you have several options of where to purchase this it has obviously been produced. You could ask where you purchased this product how long they have been selling the product and also where they came up with the design. I should also add, that I cannot even see this product for sale on their website!
I would wait for them to send you a formal letter of claim - if they do.
Do not send your product to them. However, you could consider removing them from your site until the matter is resolved and whilst you investigate this.
Alternatively, as another idea, if you do not wish to get caught up in a legal dispute you could offer to sell all your stock to them!
I hope this assists, any further questions please do let me know.