I will be in London next month. What exactly should I expect the sales person to say when I tell them who sent me. Sounds covert. :)

He will be prompted to say something along the lines of "sorry feller, I don't know who you mean". This will mark the completion of his assignment as it was intended. What is expected from you as the participant will be to nod along and move on, after completing the monetary transaction, of course. This way he will know that you have completed your part too. Otherwise there is a chance to set off a sequence of events that may be most full of misfortune for anyone involved.

Nothing. You are supposed to just go home and lick the pages.

A civilised person will know to lick the fingers instead as they touch to turn the pages.