Help to find the history of my 1900's Armstrong cycle :)
From http://www.bikeforums.net/classic-vintage-bicycles-what-s-worth-appraisals-inquiries/850018-1957-armstrong-havana.html it looks like it could have been made form 1957 to 1961 or later. It looks like it has a 3 speed internal hub gearbox, probably a Sturmy Archer, as it is British made.

Appears that Armstrong was part of a larger group by this stage, and the ealier design approach may have changed a lot.

If you look under where the pedals are (the bottom bracket), there is often a serial number which may contain the year of manufacturer. Or it could be stamped elsewhere on the frame.