Nice interesting cancellation.
I remember a while back about the thread in SCF on the different British postmarks like this and the triangular ones as well etc.
I have scanned this stamp from my collection of different British postmarks and what I am asking is this: This 'triangle' marking has only the number '779' in it, nothing else. Does anyone in the SCF have any ideas what this is? Is it a post office number??
Any information would be appreciated.