Prime Minister Theresa May's office distributed a letter to major United Kingdom companies for senior executives to sign praising her government's Brexit strategy, according to a draft seen by Bloomberg.
The European Commission will publish its first formal paper later today on how it believes Britain should deal with the Irish issues in the Brexit negotiations.
But unionists fear that the proposals would result in "the partition of the UK" and play into the hands of Sinn Fein - which is calling for a new referendum on Northern Ireland's future.
He said he was anxious by what he saw in position papers published by Britain in recent weeks, and said Britain wanted "the EU to suspend the application of its laws, its customs union and its single market".
London says the issue of how goods and people will move across the frontier can not be separated from discussion about wider customs arrangements between Britain and the European Union.
Politicians in Ireland want to avoid a hard border, for fear of separation issues that were heightened during the Troubles.More news: Report Questions When Joe Paterno Learned About Sex Abuse Allegations
The Commission's chief Brexit negotiator also made clear that the Common Travel Area regime between the United Kingdom and Ireland can not be negotiated before there is "sufficient progress" on citizens' rights and the financial settlement.
Establishment of a physical border could revive security concerns, 20 years after a peace deal involving Dublin that ended a long civil conflict in Northern Ireland and led to the end of army and police checkpoints.
The Labour peer, who was Secretary of State for Northern Ireland between 1999 and 2001, said that people are "hugely better off in the single economy that has emerged across the island of Ireland".
"That was one of the reasons I went to Detroit - not so we could replicate what there is between Detroit and Buffalo - but so that we could use some of the same techniques, [such as] authorised economic operators, pre-notification, electronic tagging on containers".
Brussels has insisted the UK makes "sufficient progress" on its financial settlement - as well as the Irish border issue and rights of EU citizens in Britain - before talks can move on to discussions over the future EU-UK trade relationship.
He will also criticize what he regards as the government's "dogmatic insistence on taking Britain out of the jurisdiction of the European Court of Justice", which he thinks could put vital European peace funding at risk.
The European Parliament can veto any agreement between the EU and the UK.