The area around Montagu Square saw a great deal of the aforementioned "action", no more so than in the mid-60s, when Neil Aspinall and Mal Evans shared a terraced house in one of the mews behind said Square, at number 16.
Them Fabs were photographed here on 1st December 1965, supposedly "rehearsing" for their forthcoming (and final) British tour. A likely story.
Still, the house has seen no major renovation since then; note the fireplace:
John and George were captured on the other side of this room, beside the staircase:
Said staircase:
Heading up said staircase, one comes to what would have been Neil's bedroom (or Mal's):
And up another floor to what would have been Mal's bedroom (or Neil's):
They weren't here long, but while they were here, this is where they were. Or something.