As above, relax!
Everything gets handed to customs for inspection, however, 99% of the time it only takes a day or so (often only minutes) to clear...
If you think of the volume of stuff coming through that Parcel Force depot in Coventry every day, they're only looking for counterfeit goods on a commercial scale which are going to be sold illegally in the UK. If you ever get a package 'pinged' it is becasue you were either very unlucky, the custom's guy was in a bad mood and wanted to pass it on, or your TD wrote "FAKE WATCH" all over the box!
I imagine they move stuff around with bulldozers in that place they've got so much to get through!