What could this scam be?

[smallglassbottle]

Just received a tatty plastic bag addressed to me, with an opened envelope, with a piece of junk mail inside. The junk mail had another person's name on and is from another part of the country (Birmingham).

The sender of the crappy plastic bag, plus contents, is based in Peterborough. I live far away from Peterborough.

Is this a money laundering thing?

I am not sure exactly how it works but we were staying in a holiday let in East Yorkshire last year and a series of parcels turned up with a variety of names on. I contacted the owner who asked me to peek inside one and it was bizarre junk basically.
I think 4 came over the space of a few days, we just put them in a shed as requested but the owner said she thought it was some sort of scam but couldn't work out what exactly

Dh thinks it's money laundering, with them keeping proof of postage in order to generate false invoices.