With the code (and Brian Sinnott), I could retrieve where this stamp was bought.
High Street Post Office, Croydon (Google Street View).
009013 designated the three Wincor-Nixdorf machines of High Street Post Office branch in Croydon, southern London. Very logical because Stamp Magazine's editorial offices are located on the 233, five hundreds meters further on the same street.
These three machines have been in service since November 10th, 2009. For this stamp, machine #3 served for its first service provided to its 5662th client session.