Do I have to stop propanolol and carbimazole before radioactive thyroid scan?

Yes for carbimazole. You should stop carbimazole at least 3 days before radioactive iodine treatment but should continue propanolol.
Stop carbimazole. Carbimazole will affect your thyroid study. You should be off of it for at least 1-2 weeks. The Propranolol will not affect the thyroid study and it will help control the symptoms of your hyperthyroidism.
Stop carbimazole.. Stop carbimazole since it can interfere with radioactive iodine uptake calculated on thyroid scan. Some institutions vary as to number of days to stop carbimazole before the scan. Some institutions say stop 48 hours before. Some say 7 days. Four or fives days should be sufficient but you could stop carbimazole for 7 days to be on safe side. Check with nuclear medicine dept. ; your doctor.