Spoiler
I just watched the B roll footage and I noticed some interesting details regarding Mallory's Whitehall office from the earlier part of the film. If you look carefully during the part where Mallory and M discuss the loss of the hard drive, you will notice that certain pieces of decoration and furniture from clasic M's office at the end of the film are present, such as the brass lions, the same guest chairs, etc. I bet the desk is even the same. However, as mentioned earlier, the actual layout of the two offices is very different, which means they are different rooms. I think that indicates that what we see at the end must be some new MI6 headquarters however they explain it. Mallory wouldn't move his entire office to a new location if his office is still going to be in a different building than the rest of MI6. What's the point in moving if he still has to get on the phone to talk to his section heads?
