Well, mmcfly, (mind if I just call you mm?), this and other threads might be old, but they're referred to as "hibernating" until something new comes along to wake them up. (And welcome to the TARDIS Builders Family, by the way.)
The lock on the actual set doors (as opposed to the lock on the TARDIS Prop doors) is certainly chrome. If you take a closer look at the other posts above, you'll see that in Series 1-4 it has been positively identified as a 60mm brass ERA Night Latch lock, and there is an ERA logo on the knob.
The lock from Series 5 onwards is definitely chrome. I don't think it would be a bronze one that was polished down to that extent as to have the shiny surface rather than the textured one, and even if it was, it would still look bronze, not silvery chrome. Even though there are no markings on it could be a Yale lock in chrome. (The shape is a perfect match to the Yale 77, 60mm lock.) The questions are: 1) since the Yale lock of that type comes in chrome (as you've shown in your image) did the BBC get one and replace the knob with a logo-less one; and 2) if the BBC didn't use a generic blank knob, then what is the best Yale look-alike?
So it might be a chrome Yale lock - possibly with a BBC-specified plain knob - or it might be a Yale clone.
Dino.