I called the courier company yesterday and they flagged the issue with customs. Basically all they wanted was my name, what was in the package, and my address. Once I confirmed this they said they'd release it. That was around 11am - 12pm yesterday.
Since then I kept a careful watch on the tracking status to see if it's updated. It had not updated by 9am this morning so I phoned up again. The courier company confirmed that they had put in the release request before the cut off period, they then contacted customs at the airport, an I was asked to wait a couple of hours for a return call from the airport directly.
Since then the guy has called, I've taken down his name and telephone number, and he's confirmed that he's now got all the details, apologised for the delay, and told me that I should receive the package tomorrow.
So I'm going to wait until 9am tomorrow and see if the tracking data changes, if it doesn't I'll call the guy back and find out what's going on. So here's keeping my fingers crossed! Of course I won't know what extra hoops I'll need to jump through until I've got the parcel in my hands, or it's confirmed as being within the UK transport system at least.
On a completely different note I won a ZX spectrum +2 off ebay for £7.50 last week, that should have turned up the day before last! So it doesn't seem to be a good week for me and parcels