What do you mean?? the only NCT I can think of is the National Car Test and if you are taking a car to a NCT centre, of course you'll have to have it insured.
If the car isn't insured and you want to put it through NCT to see if worth insuring and putting on the road you could always ask someone who has an insurance policy to do a temporary substitution onto their policy and drive it to the NCT centre for you.
(ps...avoid Blarney NCT centre, have heard nothing but complaints about it lately, cowboys by the sounds of it I hear)