Just received a very nasty threatening letter. The envelope has the time and date on it plus a number 34108674 - does anyone know if this is a reference to where it was posted?
Perhaps I am putting you totally on the wrong track. However the number which you have quoted is a Company Identification for a firm in the Netherlands. :-
Lankeela - does it have a postage stamp or is it franked? If it is franked, the number you have quoted could well be the franking serial number which can be traced by Royal Mail. The serial number tends to be under the amount of postage.
Seriously Lankeela - I would take it to plod. I've had one of those once, it really upset me. Despite the fact that you know, deep down, that the threats are a load of bunkum. The police will listen.