Philatex Spring 2012 - Bath No.1 Receiving House ?

I've just come back from Philatex, a fair specialising more in Postal History than Stamps that has been held twice yearly in the Royal Horticultural Halls, Westminster.  I had a very successful time, managing to spend somewhat more than my "allowance" in less than an hour !  Unfortunately I gather this was probably the last fair as the venue has been sold and will no longer be available.

One acquisition is a bit of a mystery to me - it is a Bath Penny Post from January 1836 (no day of the month in the penny post cancel, dated 19th January in a Bath double-arc cancel on the reverse) with an unframed "No.1" cancel. 

 I presume this is from the Bath Receiving House, but which one had the "No.1" cancel ?  The address inside is Beckington but according to Oxley Beckington was No. 6.