There are two Post Office objects here: https://www.openstreetmap.org/way/1105246191 and https://www.openstreetmap.org/node/331175883 . 

https://tbrooker.co.uk/bucklersbury-hitchin suggests the PO is within the Brookers store.

Survey needed to determine exactly which building(s) Brookers occupies and to consolidate the PO into a single object. #surveyme