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Gratitude; The Goldsmiths. Co.UK &Assay Office London database; and I am pleased to let you know that the makers were a firm known as British Commercial Transport Company Limited. They first registered their mark in 1925. I received this answer by email in 2010 but forgot to share it with the forum.
London year letter N for 1928
https://www.silvermakersmarks.co.uk/Dat ... -1935.html
https://www.thegoldsmiths.co.uk/
Peter.