www.bbc.co.uk/news/live/election-2019-50683887
12:08
Highlights from the Northern Ireland document
Chris Morris
BBC Reality Check
This Treasury document sets out things that trade experts have been saying pretty clearly, but that the government has refused to accept lied about.
Under Boris Johnson's EU Withdrawal Agreement, it says, customs declarations and documentary and physical checks on trade between Great Britain and Northern Ireland will be "highly disruptive to the Northern Ireland economy".
The document notes that 98% of businesses that export to Great Britain are small and medium businesses that are "likely to struggle" to bear the cost.
None of this is a huge surprise to anyone committed enough to have read the Protocol on Ireland and Northern Ireland carefully, but it is not what the prime minister has been saying about his own deal.
Another striking line from the leaked document says the Withdrawal Agreement "has the potential to separate Northern Ireland in practice from whole swathes of the UK’s internal market".
That is why, in a nutshell, Boris Johnson lost the support of the Democratic Unionist Party in Northern Ireland; and it was his lack of a working majority in Parliament that led in turn to this election.