msummers, 12AU7 and CV4003 are two different names for the same tube. 12AU7 is the American designation and CV4003 is the British designation. ECC82 is the European designation. There are also many variations with other names, such as the Amperex 7316 or the Mullard M8136, that are basically the same tube.
Most Mullards were made at the Blackburn plant, with the Mitcham plant coming in second. Tubes made at other Phillips factories were often labelled Mullard, though.
Brent Jessee has a lot of information about tubes on his website: audiotubes.com, including how to read Phillips tube codes (see the yellow box entitled "Euro Tube Codes"), which will tell you where and when your tube was made, whatever it is labelled.
Check out his website and if you have more questions, which you probably will, feel free to ask. I would start out by reading up on the 12AU7 by clicking on the the yellow box with that title.
