In reply to George Fisher:
All a bit of a guess as given the circumstances, and it’s been a while since I had up to date info, but based on the usual for undeliverable items by Royal Mail I would assume something like:
If it goes by Royal Mail and is not delivered (logically as it may be stopped at the PO Box stage and probably wouldn’t be delivered if RM check the account details as the pre paid envelope probably won’t be paid from an account of a collapsed company), it will then go to the RM National Returns Centre in Belfast. They will open and as your details are inside it will be returned to you (you’ll probably have to pay postage as none would have been paid in the first place would be my guess). This all takes time and can be at least 3months, if not considerably longer.
If it’s very recently you posted, you could try and attempt to contact the RM local delivery office for the town the company is based. They wouldn’t open and return direct, but it may prevent it being delivered somewhere if the company is still getting mail, and they could forward to their Returns Centre.
If it is delivered that will be up to the company to return it. It seems the company is still “active” on the Companies House register (though that could be an admin delay); could it be a temporary blip in trading or do you think it’s permanent.
If you know someone in the same town as the company, get them to check the door of the company for any posted info which may have contact details or some reassurance that items will be returned. Alternatively, if you know some contact details (phone, email) would be worthwhile attempting contact.
HTH.