IoN is a multicentre phase II/III asking is ablative radioiodine necessary for low risk differentiated thyroid cancer patients. 560 patients will be recruited and randomised 1:1 to receive radioiodine ablation or no ablation. Samples collected during trial: Stimulated Tg blood samples for patients taken at the treatment visit, 2 months post treatment, 6-9 months post treatment and every 6 months thereafter for 5 years.