
Source
Postal cancellations of London by Westley.
Not that I was au-fait with the example,

it's nice to see postmark queries,
one learns when responding, like this postmark could also be
confused with a Type 12 "too late" strike,
the bars are identical, however the too late did not come with
the numeral 50.
Fascinating stuff.
Note also the "toning" from the linseed oil in the cancelling ink.