Kev,
  Many thanks for that... I looked at SCR devices, but concluded that they'd ****** up the supply. One more question...do you reckon getting a 2nd hand variacs worth while? I've seen one on ebay which would mean I wouldn't have to build a case for a Maplin's one   
http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA%3AIT&rd=1  Thanks again, Ian