In Peaky Blinders s03e06, after kidnapping Charlie, Father Hughes tells Tommy that he knows everything about his plan including digging of tunnel to steal jewels from the Russians, and the plan he hatched with the Soviet diplomat to not blow the train.
Later, Tommy confronts his family in order to know who he/she was who gave away insider information to the priest. Everybody denies doing that. Polly however believes that she might have told Ruben under the influence of wine.
At a later stage, Polly calls Ruben to their company in order to confront him (and maybe kill him as well). But they don't talk about it all. Instead, she says that she wants a normal life with him.
Who, exactly, sold the information to the priest?