This looks a bit like the design elements in the 1881 series listed in Forbin; unfortunately, the 10p design is not pictured...only two of the eight values are pictured.
If that is what this is, it is the lowest value (Forbin #1) of the set. The stamp size would be 28mm by 45mm, and it would perf 12.5.
Not much value in Forbin, but that was 1915.
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