Well, he is asking for someone who listens to Manchester, to pass on the next freq that the crew of the London bound plane will receive. That can only be done if the 'user' is listening to the scanner and hears the next freq and posts it here. In my book, that is passing on information heard on the scanner which is illegal regardless whether he is going to listen to it or not!
As I said though, I would go and post on the ATC forum and ask for a Manchester controller what the next freq will be.