You need a licence to watch any live tv service. The law was changed in 2016(?) to add BBC iPlayer catchup services. It doesn't include other channel's catch up

You need a licence to watch any live tv service. The law was changed in 2016(?) to add BBC iPlayer catchup services. It doesn't include other channel's catch up service, so you don't need a licence if you only watch catch up on 4OD.