I know there are threads about shipping to the UK from the U.S. over on British Blades. Might be worth a look since things change and I know that I read folk there saying that a change in post handling meant that fewer locking folders were getting confiscated by Mount Pleasant (Mnt. Doom) at one point, but that too might have changed again. Missing through theft is one issue, and missing through Customs confiscation is another. The inspectors for FedEx,UPS, DHL etc weren't the same as for USPS-Royal Mail/Parcel Force.
Regarding tracking, I don't reckon the tracking service offered by Royal Mail and USPS is worth squat. I sent my tax returns to Austin TX using RM with full tracking, but when it gets to the U.S. the service is handed over to USPS along with tracking. USPS decided that no such address existed and that my package had no return details...tracking told me it was being held in Austin and that was the last I saw or heard about it. Nothing I could do, hours on the phone being passed around but no one could tell me how to get my pack back. Resent with DHL, printed address from same file and it was delivered correctly no mess, no fuss. Reckon you would have the same problem tracking a valuable item heading east as I did going west