I was called at the end of the auction by East, who asked to speak to me away from the table. He said he'd found out that 2♦ was an artificial relay but hadn't been alerted. Had it been alerted he would have doubled to attract a diamond lead.
I expressed surprise that he didn't know the likely meaning, and he admitted that he did know it was likely to be a relay, but he couldn't be sure, and he felt he couldn't ask and find out it was natural. (He claims he does know pairs who play this as natural.)
I told him he had to go back and play the hand out. He couldn't insert a double retrospectively into the auction. I would look at the hand at the end of the session.
West led ♣6. and declarer made 12 tricks.
Some more information: 2♣ was artificial, 23+ pts balanced or GF. It was alerted. 2♦ is commonly played as a relay or an artificial negative response. It should have been alerted, but wasn't. Players are often lax at alerting such calls when "everyone knows what they mean". South freely admits he should have alerted it, but says he was concentrating on his hand. (Don't ask me why North did not bid Stayman.)
Are EW entitled to any redress?