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Assuming that it is in fact a London mark (without an image of the rest of the hallmark we cannot be certain) there is still a problem in that the date letter is indistinct - it may be lower case letter "l" for 1866. TJ would probably therefore be Thomas Johnson.
That will be the assay office mark (uncrowned leopard's head for London) and the lion passant for sterling silver. When the image is inverted the assay office mark is much more obvious.