Any 'deal' the US might make with the Blair govt is a moot point. Tony is on his last legs as PM; he and GW are both lame ducks, but the Blair regime is closer to its end than Dubya's.
In either event, the U.S. holds the bargaining chips (Iranian prisoners) and I doubt we are going to turn them over to Iran for nothing. As harsh as it sounds, they aren't our boys.
Maybe some of the Iranians we hold will end up being part of an eventual deal for the release of the 15 UN sailors, but I guarantee the U.S. will get something out of it.