Non-PRO English Art/Literary General / Conversation / Greetings / Letters London accent (or Southern English pronunciation)

Hello!
The expression is taken from a George Orwell article published in 1945 in the UK weekly, the Leader Magazine. Orwell complains about the state of pronunciation in the south of England, including London. He gives a couple of examples, I only quote part of the paragraph:

"Most of us now speak in so slovenly a way that if you ask for a threepenny bus ticket you are as often as not given a three- halfpenny one, or vice versa. And how exactly would one write down the mystic formula which any two Londoners invariably utter after concluding a transaction? The nearest you could come to it would be “nkew,” or perhaps simply “N.Q.” Or take the current pronunciation of such words as “passionate,” “deliberate,” “vegetable,” “actual” or “average...”

Does anybody know what this "mystic formula", or "nkew" is about? And can you give a more explanatory context than the "concluding of a transaction"?
Thank you.