thelewisgang ...I dont think Brabantia will use the same pattern lock for all their post boxes....The best thing you can do is replace the lock and it will come with new keys.
brabantia dont seem to list the lock as a replacement part, but auzzie has given you link......
Dont want to worry you vivandron...I've got some keys lying in my van that will more then likely open you or your friends front door... especially if its a door with a Euro or a Yale type Cylinder. I use them whenever I need to gain access to a property, and no keys are available.( 12 of these Keys will open most UK cylinder type locks)
They are not skeleton keys, but they are readily available, as are all the tools to open almost any lock you could care to mention.
The tool needed to open most 2..3..and 5 lever mortice locks (in the UK) is also easily obtained..and it works !
When I need to force an entry...most doors are fairly easily opened as long as they dont have a mortice lock engaged...........Sleep tight.!