"The reason we signed the agreement was to ensure Brexit", Mrs Foster said on October 1.
So yesterday was either a very good day or a very bad day for Theresa May.
Prime Minister Theresa May issued a stern warning to the European Union in September - insisting the bloc would be making a "fundamental mistake" to think Britain will accept an arrangement that would "break up" the United Kingdom.
In his letter, obtained by The Sun, Mr Davis said that the European Union was likely either to reject the Chequers proposals at next week's crunch summit in Brussels, or to demand "further significant concessions".
She said regulatory checks as part of the backstop could mean Northern Irish milk being processed in England and turned into yoghurt or protein drinks facing checks when they came back into Northern Ireland. It is something I will ever agree to.
Top EU officials were warned Wednesday to make plans to cope with the fallout from a "no-deal" Brexit as their chief negotiator said talks with Britain must make more progress before next week's crunch summit.
Among those due to attend today's War Cabinet are: the Prime Minister's effective deputy David Lidington; Jeremy Hunt, the Foreign Secretary; Sajid Javid, the Home Secretary; Liam Fox, the International Trade Secretary; Greg Clark, the Business Secretary; Michael Gove, the Environment Secretary, and Gavin Williamson, the Defence Secretary.
But Cabinet sources said senior ministers were expected to consider the backstop plan when they met this afternoon with a view to getting the backing of the full Cabinet next Tuesday.
Mr Barnier said: "Our proposal is just a safety net, the backstop".
Pressed if the DUP would veto any EU-UK agreement on the backstop, Mrs Foster said she would have to wait to see the detail of any text, and would not comment "in a vacuum".
"It is needed because the detail of the future withdrawal with the United Kingdom will only begin after the United Kingdom withdraws".
The spokesman said the "meaningful vote" promised to MPs would cover not only the withdrawal agreement but also the political declaration on future relations.
And he told fellow MPs: "If we stay on our current trajectory, we will go into the next election with the Government having delivered none of the benefits of Brexit, with the country reduced to being a rule-taker from Brussels, and having failed to deliver on a number of promises in the manifesto and in the Lancaster House speech".
The DUP have repeatedly warned they will not support any Brexit deal that could lead to new economic barriers between Northern Ireland and the rest of the UK.
Barnier said he realised such checks were politically hard but this was the effect of Britons voting to leave the EU.
However he said other products could be dealt with by scanning barcodes on lorries or shipping containers.