Hiya Rose,
This is a Michael Harris design, produced from early on and still produced today - it is currently called "Crystal Blue Stripe" by the factory.
But yours is a lovely earlyish one - probably mid-'70s from the script of the Mdina mark.
I don't think they produced this shape so often later on.
It's a flanged bottle. The flange is quite wide - so definitely post-Boffo arrival!
The "crizzle" effect is produced by plunging the gob of hot clear glass into cold water, then silver chloride salts are introduced into the cracks that appear. Then it is decorated with ribbons of teal glass which are marvered in and then it is cased in more clear and further blown and shaped.