Thanks Mark and Gasman 1 UK!
 It is a grey button but the part number differs from Mark's info - namely Honeywell ST7100.
Does this mean that we CAN get the part or repair/clean it up [I actually mean my CORGI registered plumber] 
Your further expertise and advice would be most welcome.
PS - have you a contact for Atwell UK please?
                
 Scarletta
                
 November 2008