From Nigel Brown's book. He lists him as Alexander Thomson (without the 'P'). Gunmaker 3, Drummond Street, Edinburgh 1820, 16, Union Place 1833-c.44. also at 3, South Street Andrew Street, 1840-41. Alexander Thomson & Son 1869-75, 3 Hanover Street 1876-c.78. He goes on to list a further 5 Thomsons trading in Edinburgh at various times who were almost certainly related in some way.

A very nice find Mike. Lagopus.....