...we also taxi our 319's on one engine, but only taxi in.
In the SOP's it is permissible to shutdown engine 2 cos the APU and Yellow pump can supply the Yellow hyd system.
On the 319 only we can shutdown eng 1 (obviously not after shutting down 2 first) if we need to park at fixed pier stands as eng1 can get within 6ft of the pier in some cases.
At BA at LHR we have 50 or so 319/320's and very often taxi on one engine so if flying BA to Europe it is likely that you could here the PTU.