Mark I dont think it's changed much particularly on the river Lea according to the Book : The London Anglers Book: Or Waltonian Chronicle - published in 1834 Which is one of the books that Maggies shortcut above points to. According to this you have to shout “LAW!” each time you want a pee, otherwise you chance getting your throat cut.
Extract from above book:
‘BOBBERS LAW’
There is a rule or law practiced by the London Anglers, particularly those who fish in the Lea, which is that of waiting for any of their party that may drop in the rear, it arose from the following circumstance:
Some years since several Anglers were proceeding on a trolling excursion to a favourite spot at some distance from London, up the Lea river, when it happened that one of them, without being observed by the rest, loitered behind, and his absence was not discovered till they had travelled a considerable way; they waited in hopes their companion would overtake them, but his not coming up,they halloo’d and called him by name, but received no answer, alarmed for his safety, they retraced their steps, when to their utter astonishment and horror, they found him quite dead, with his throat cut from ear to ear, and robbed of every thing he posessed; it is supposed he staid behind for a natural purpose, and was attacked and murdered while in a defenceless position. Since this lamentable occurance, if an Angler has occasion to stop, he has only to call out the word, “Law,” and the whole party wait till it is convenient to continue the journey.
