We now know that the "signatures" are not any of the glassmakers, but added by either Eric Dobson or Marie, who was the niece of Vicente Boffo.
They were added to the more upmarket pieces, such as this facetted cube solifleur, to appear that an artist had signed them.
It still means that this is a piece highly rated by the factory.
This isn't a Michael Harris design per se, but an adaptation of his Cut-ice lollipops design; it's just made into a different shape.
They were not made for a particularly long period of time, mid 70s to mid '80s.