How old is this silver plated salver

I have just bought this and I am puzzled because the design goes right through to the back like some modern silver. I am pretty sure it is antique, it also has an armorial which I cannot completely identify, could be Watson or Wentworth they both use the motto mea gloria fides. There are no makers mark but a scratched mark in the centre back which could be an inventory mark?[/img]
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