Thanks for the suggestion Anne
Now I look at it, it could be a Maltese cross. My OH thinks its plated, but I'm not so sure (may be wishful thinking
) I'll continue a search including a Maltese connection, and see what I can come up with. If I do find it, I'll get back. Might just take it to my local friendly jewellers just to see what its composition is, although I doubt that they will recognise the markings (but you never know).