There were a lot of silversmithing courses around at night schools in the 1970's. Could this be the source? It does not look like a professional piece.
That seems quite likely. The spoon is very poor quality and the mark GEM has been stamped three times. I'll contact the London assay office about this one.
The assay office replied very promptly to tell me the mark could be that of Gillian Elizabeth Mallett who first registered in December 75 and is still registered.