I’ve replaced the footswitch with the 3pdt footswitch above. Although I haven’t yet taken it out for a gig (for a real test) this seems to have done the trick!
Thanks for your replies guys. I have ordered a replacement 3pdt footswitch (from here: http://www.little-black-box.co.uk/components/3pdt-true-bypass-footswitch/prod_21.html – as it seems to be the culprit) and hopefully will have it sorted out soon.
Cheers,
Saulo