Thanks for replies, chaps.
Trevorh – a reducing sleeve might just work, except that there is restricted throat distance on my mill which could "reduce" its usefulness. The edge-finder is a pretty meaty bit of kit as it is!
Robbo – I, too have used these suppliers on a number of occasions. In fact the collet set that I use all the time came from there. I feel another vist to their web site coming on!
Martin W – You are quite right, of course and it would just exacerbate the lack of throat distance. I also have one of the spring-loaded edge-finders. Works OK but I like gadgets!
Problem solved, I think – I'll order a chuck and collets from CTC tonight!
John