The route from the escape ladder from a mezzanine floor is partially blocked with pallets of stored stock with just enough room for a small person to pass through, I am 8st7 and 5ft1, is there a minimum clearance required for escape routes?

The Approved Document B states the narrowest width would be 750mm but post war building studies looked at a single exit width being approx 525mm, so long as people can walk out single file comfortably (not having to turn sideways or anything) there would be very little difference (if any) between the evacuation times through a 750 door. IIRC correctly the old blue & primrose guides etc allowed 550mm widths in certain circumstances. (Small numbers of employees or something like that) I would say, considering the average size of people today compared with the late 40's I would accept the latest guidance 750mm but after a considered risk assessment I may accept 650mm.