Wasn't planning on posting about this before, but well, UP{S deserve this. I actually had 2 calls from UPS Brokerage East Midlands Airport after my parcel was delivered. They were very adamant that I needed to check an email that they had sent me, fill it in, scan and email it all back to them.
Trawled through my emails and turns out they were customs clearance forms that were needed to release my parcel from customs so that it could be delivered to me. Only thing is (I'm sure you can see where this is going), it had already been released, delievered and retrieved by me.