The Widebeam GRP composite Mirror had a GRP hull, skeg, bilge pieces and wooden interior (decks, bulkheads, side tank panels, thwart, daggerboard capping, transom doubler). Hull was chopped strand mat and they were heavy, so best avoided if you want performance.
The Bell/Ferranti GRP Mirror never took off and I understand Widebeam introduced (?) this boat in attempt to move towards GRP with a competitive boat. I'm pretty sure Tim Grey raced one on the Mirror circuit in the 1990s, however, they were still too heavy for racing success.
Here is a list of some examples