The British government must have been aware of the DUP red lines around an Irish border as its raison d’etre is to keep the UK together
The whole point of the DUP is to safeguard Northern Ireland’s position within the UK. As unionists, they believe in the nation state and see the UK as the rock on which our prosperity, security and identity is built. It is unsurprising that these views have lead them into a strongly pro-Brexit stance, though even then there is a pragmatism to their politics that is sometimes missed. The government would have known what the DUP’s red lines were before the latest round of talks hit the buffers.
The Irish government denies the charge that it asked that Monday’s Brexit paper be kept from the DUP, but the reality is that the DUP had received only an emollient verbal briefing and had been asking for days to see a paper. It was passed to them only as Theresa May was going to lunch in Brussels; the frantic phone calls that followed stopped the deal in its tracks.