The style of the lion passant and date letter indicate that the pendant was assayed in Birmingham during the 1925/26 assay year. I do not think that the mark on the left of your picture is a maker's mark. Are there matching marks on the case?
The case was made by the Dennison Watch Case Company, a Birmingham company founded by Aaron Lufkin Dennison. It was assayed in Birmingham in 1926/27. It was not uncommon for the pendant to be made separately and bought in by the case maker.