I was mooching around Tescos this evening and I noticed that Birds custard powder is, in fact, sugar free. It's only the added sugar when it's made up that makes it unsuitable but if it were made using Xylitol ( also called Xylobrit, Sorbitol and so on ) then it would be suitable for diabetics.
I am aware of the laxative effect of Xylitol and so on but in moderation it's fine and it reopens several doors, like my wifes home made ice cream for example
Just thought I'd mention it.
G