okay,
it's NOT the Columbia:
http://www.lathes.co.uk/columbia/
But it sure looks like the Zenith:
http://www.lathes.co.uk/zenith/
I think that's it!
the vertical dovetails look identical
the rotating bar thru the head for the motor mount looks identical
the cast splines on the motor mounting plate are very similar, your plate is bigger
it agrees with the #10 B&S spindle taper
even the "louvres" on the box base look right.
-brino
EDIT: the most noticeable differences I see are:
1) what I believe is the spindle lock handle. The Zenith mill on Tony's site has the lock handle towards the front of the spindle column. On yours, that handle is in the middle of spindle column.
2) The one on Tony's site has the name "Zenith" right in the casting. Yours seems to be missing a plate that had the manufacturers name.