Anything from outside the EU will get diverted for Customs clearance (and VAT charges if it's more than a few pounds value).
If they think it's anything illegal or covered by import restrictions, it could be impounded / destroyed, or they may contact you for more information.
Other than that, you should just get the item, or if there is a VAT charge, a form letter asking you to pay the VAT.
Parcelforce have email contact info on their web site (link below). Email them ask them what the status of your item is, giving the tracking number.
http://www.parcelforce.com/contact-us
It means someone from the royal mail stole it from their international hub. It also means you will never get it now so you might as well lodge a claim for compensation with royal mail and keep your fingers crossed that they pay you what you claim.
Ring them up. This happened to me and it turned out that I had to pay a fee to get it to me because it had to go through some sort of process before it was aloud to be processed anymore.
I ordered something from china and it got to the UK in three days then it got to international hub and everything was processed and the last update said recived and processed and in progress and its been like this for 12 days! Im getting really annoyed and worried right now. Please help me and thank you!