Interesting! Is it a rare postmark?
Probably a good idea, to scrap the word "rare", a very badly over used
philatelic term. "Scarce" is more amenable.
Probably not, as we see, it has been in service, at least 2 years
in a very populous location in London.
We would expect to see many examples.
That said, I cannot find any reference to it anywhere in my records,
(still looking) but that does not mean it is scarce, just poorly reported, Postmark collecting is not a major discipline for many collectors.
If it were scarce, that may not translate to any great value either.
Certainly a curious postmark, and a post office yet to be discovered by me, in print, anywhere.