Who is Jerry Westerby from Tinker, Tailor, Soldier, Spy and what is their importance?

Jerry Westerby is a sports journalist. Since his job required a lot of travel, he often did small jobs for the Circus. When he was in Prague, he heard a story about Ellis from a man who was in the army. The Russians had been waiting for the British agent. He relayed the information to Toby Esterhase who said the story was a plant and wouldn't even allow Jerry to write the story for his newspaper. Westerby sent the information to Smiley via letter. Westerby hasn't had any assignments from the Circus since his last meeting with Esterhase over a year ago.