Thank you Silvermakersmarks. The stamp looks like P&M shown in silvercollection.it. For electroplated they used additional marks, which are absent on the piece.
PARKIN & MARSHALL
Sheffield
Active at Telegraph Works, 23 Furnival St, (1770-1892), Sylvester St, (1893-1914) and Milton St, Sheffield (1915-1924). The firm started electroplating in 1861. The firm used the trade mark XL ALL and SHARP EDGE
I have just tested deep scratch with acid and oxidant. It remained bright bloody red with no signs of blue, green, yellow or turquoise for that matter. Could it be the piece before 1861?