Hi and welcome to the forum.
You don't seem to have figured out all of the marks as this is a Sheffield hallmark not London, under which you originally posted your query. The date letter T is of course for 1993. Unfortunately we do not know the identity of EI although I have previously seen the mark on a 1990 frame so we can assume that EI probably specialises in frames. The Assay Offices do not, in general, publish identities relating to their sponsors' marks but are often happy to answer individual queries.