The next day Ian Holmes reminded me of a jug he purchased last year. It has a mariner's compass transfer signed 'J P. Newcastle and North Shields' (see below left detail). Ian Sharp has a jug with a very similar mariner's compass transfer on his website, but it is signed 'J C. Co N Shields' (see below right). The '&' appears to be obscured by a break in the transfer.
It seems clear enough that the right detail refers to the John Carr & Co partnership of c1850–1854. The left detail is more confusing. It must have been engraved after 1848 when the Carr and Patton partnership dissolved (or else why aren't both sets of initials on the transfer?) and John Patton took over the Phoenix Pottery, Ouseburn (Newcastle). But it suggests he still had some stake at the Low Lights Pottery in North Shields after that date. Perhaps with the Phoenix Pottery being a new venture for John Patton, he simply wanted to make clear he was the same J P who'd worked in North Shields for 15 or so years.