For anyone following the UK political developments in recent months, the role of the Speaker of the House of Commons, John Bercow, might have received special attention. His calls for "order, order" are particularly well-known.
The question is simple. Is this call for MPs attention the (only) official way to do so? Or is it merely a custom which depends on the style of the speaker? For instance, could he instead use words like "attention", or "silence", or etc?