Opinions regarding possible counterfeit marking taken from images alone are always a minefield, so I will just point out the parts that to me would set the alarm bells ringing.
1, 2, - The spacing of the letters within the cartouche does not appear to be uniform.
3, - This cartouche shape is to be found on small objects only.
4, - What is this 'misting' around the marks? Have they been recently struck and then buffed up?
5, - Where is the Leopard's Head mark?
6, - A small point, and perhaps not valid, I would expect the Storr workshops to have been a litte more careful with the application of their mark.
One could also bring into question the shape of the 'PS' cartouche with its somewhat flattened sides.