I'm travelling from Worthing to Taunton via London on a return portion of a super off peak return ticket, but want to get off at Clapham Junction and use my Oystercard to travel around London for 2 days before continuing my journey to Taunton from Paddington. My question is, can I tap in within the barriers at Clapham J after getting off the train from Worthing, or will I have to exit the gate line and tap in with my Oystercard?