Preheat oven to 140 C / Gas 1. Place jars and lids on a baking tray or in a tin, then place in the oven for 10 minutes. Keep the jars and lids in the oven until ready to use.
If you're using Kilner-style jars that have a rubber seal, do not sterilise the seals in the oven. Boil the seals instead, as the dry heat from the oven can ruin the seals.