Ok, managed to get a bit of work done here
I made a stain using oil paint thinned out with white spirit. This i did twice as i was not happy with the first colour.
After this i dry brushed/stippled on various shades of grey and blended out any unwanted splodges etc with a clean brush dipped into the white spirit. Basically i just fannied about with it until i got the effect i was after.
Sav