In the coming days, markets may probe and call the bluff on Boris Johnson's threat to crash Britain out of the EU, setting up a full-blown currency crisis well before the Brexit deadline he has set to get out with or without a transition deal by Halloween.
The political game of chicken his weak administration is playing with the EU may turn into something else -- a political and economic crisis with currency markets testing which of the two blinks first. Sterling hurtling to new lows against the dollar and towards parity at 100 pence against the euro is something Mr Johnson and his jittery DUP just cannot ignore.
However, the stakes in the coming weeks will be raised significantly for Irish business and the Government too.
The damage that a slump in sterling can visit on Irish business has been thoroughly traced ever since a majority of the English and Welsh electorate voted to leave the EU just over three years ago. Immediately after the outcome of the June 2016 referendum, sterling slumped by up to 15% -- effectively meaning that UK citizens got a lot poorer very quickly.
Trading at around 73 pence against the euro on the eve of the vote, the UK currency slumped in short order to 81 pence; traded at 88 pence when the former Prime Minister Theresa May conceded power to the Brexiteers; and strengthened all the way back to 80 pence when she struck a withdrawal or transition deal with the EU that included the Irish backstop and its guarantee of no return to a hard border here.
But sterling slid again when the nomination in the Tory contest of "do or die" Mr Johnson as prime minister became a racing certainty in early summer.
Sterling is also a key indicator for all sorts of reasons for the health of the Irish economy -- north and south. But the overriding reason is straight forward: The 60 million-odd people living in Britain is a huge and irresistible market for any business trading on this island of 6.6 million.
Britain is also the landbridge by which all sorts of Irish goods, including dairy food products and pharmaceuticals made in Munster and airplane parts from east Belfast, get off the island in the cheapest possible way for delivery down through the English channel ports to a much larger market on the continent of hundreds of millions.
And this snapshot of trade in physical goods doesn't even come close to covering the billions worth in services, including insurance, banking and tourism, invisibly sold both ways across the Irish Sea into Britain and beyond - all of which requires a predictable and steady exchange rate that sterling once was.
However, for the Irish Government a sterling crisis would likely bring it another headache in the form of plunging stock market values of the Irish banks.
The fate of the UK currency and the shares of Bank of Ireland, AIB, and Permanent TSB have been linked ever since the June 2016 vote. Damaged economies in Britain and Ireland that a crash-out Brexit entails, weighs on the future earnings of Irish banks and puts back their recovery plans from the all too recent banking and property crash.
Sharp falls in bank shares is an important signal which cannot be brushed aside -- as some Irish bank chiefs here have done in recent times by talking up the issues facing all banks across Europe.
Brexit is the first real-life stress test for the Irish banks since their €64bn recapitalisation was completed in 2011, and evidently, for investors. it has already laid bare the lenders’ underlying weaknesses.
And this despite the Irish banks having had something of a charmed life in recent years.
An extraordinary level of write backs boosted earnings and led to pledges to investors of large dividend payouts in the future.
Those write backs were based on an unsustainable surge in house prices driven by a dysfunctional housing market, while the Government and TDs have given in so readily to initial push back to selling off soured loans -- which shrinks loan books and weakens the banks’ power to generate future profits.
Bank of Ireland trading at €3.33 on Friday have dropped at an alarming pace as Mr Johnson stuck to his plan to steer the British ship into the Cliffs of Dover. The shares have lost an extraordinary 55% of its value in the past year. AIB trading at €2.70 have dropped 44%, and Permanent TSB shares at €1.11 at the close on Friday have lost 47%. They are losses no one can ignore.