Sterling fell against the euro and the dollar as the political machinations in Westminster brought the likelihood of a general election much closer.
The UK currency fell to 90.90p and to $1.208, but shares in Dublin and London were mixed.
Speaking after a cabinet meeting, Boris Johnson targeted potential rebel Tory MPs not to sabotage his negotiating threat to take Britain out of the EU without a deal.
Conall Mac Coille, chief economist at Davy, said Britain is heading to an early election "one way or another".
But whether any election takes place in October or November "remains to be seen", he added.
“It looks increasingly like the UK is headed towards another election,” said Chris Beauchamp, chief market analyst at online broker IG.
The next few days promise to be a crucial moment for the UK’s political direction, but sterling is taking it badly, dropping against the dollar to towards the August low, a move that is unlikely to stop there.
Mr Beauchamp added: “Anyone who thinks that an election will solve the UK’s political crisis has not been paying attention over the past three years.”
Manufacturing surveys on both sides of the Irish Sea showed activity had slowed because of Brexit at a fast clip.
The survey of purchasing managers at Irish factories showed the US-China trade wars had also weighed on orders.
Among the Ftse 250 companies which are the most exposed to any downturn in the British economy, Hammerson, -- the owner of Brent Cross shopping centre in London and Dundrum Shopping Centre here -- slid by 2.5%, but other British property shares such as housebuilder Bovis gained 1%.
Irish shares were also mixed, with AIB losing some ground and Bank of Ireland gaining slightly.
Cairn Homes rose slightly, while Dalata Hotel Group slipped by almost 1%. Both companies report first-half earnings later today.