Former Northern Ireland secretary Peter Hain has said that the DUP, while being the biggest party in Northern Ireland, "doesn't speak for the whole of Northern Ireland".
Speaking on BBC's Today programme, Mr Hain said: "The DUP doesn't speak for Northern Ireland. It may be the biggest party, it's entitled to have its views respected, but it doesn't speak for the whole of Northern Ireland.
"And what Boris Johnson is doing, as Theresa May did before him, is putting himself in the pocket of one party. And that relinquishes an honest broker role. And that is very dangerous.
"The solution is to have the same rules either side of the border for customs and trade and standards and regulations.
"That would solve the problems. The problem is the hard Brexiteers, including the DUP, won't allow it."
Mr Hain said: "The other joker in this pack is effectively leaving the DUP with a veto.
"Whether the arrangements get up and running at all for a common regulatory trading zone for all goods and agri-food, livestock and food produce and so forth, whether that actually happens is up to the DUP.
"And that cannot be right. It should be the decision of the whole of Northern Ireland's politics on a cross-community basis, which is the essence of the Good Friday Agreement."
Mr Hain said he did not find Dublin's response to Mr Johnson's Brexit proposals surprising.
"Because effectively what Boris Johnson's proposal is doing is dumping the problem on Dublin.
"It's saying 'We won't put up a hard border infrastructure on the UK side of the Irish border, but you do your worst'.
"And the Irish Government will have no choice if the proposal is somehow accepted, or certainly if no deal falls out.
"It'll have no choice but to put up infrastructure for security and checks because it's the external border of the European Union and World Trade Organization rules, international trading rules, the legal situation will require them to do it."
Mr Hain said: "Two thirds of Conservative members and apparently two thirds of Leave voters, according to the polls, don't mind if there's a hard border, unless they get Brexit.
"But that is a reckless and irresponsible attitude, because the island of Ireland has been responsible for some of the most terrible terror, not just on its island but also visiting Great Britain.
"This is a very dangerous situation. And I sometimes think in the way that the Conservative Government - I'm not making a party point, I'm making a fundamental point about understanding, and Sir John Major, the former prime minister, has made a similar point - it hasn't seen itself as an honest broker here.
"It's seen itself as captured to one particular party."
'Clear final deal'
Speaking about Mr Johnson's Brexit proposals, Home Office Security Minister Brandon Lewis told BBC's Today: "From our point of view it's a final offer.
"But we are open and understand the fact that the EU may come back and say 'Look, this deal is fine, but can we just look at this...?' and we'll have to look at that when we get to that point.
"But I've got to say, to be frank, as the Prime Minister said, this is our clear final deal.
"We think it's a good deal, it's a fair deal, it delivers both legally and security-wise for both our country here in the UK and obviously our friends in Europe."
Asked if the Government is willing to enter into negotiations, he said: "From our point of view, this is the final deal, but we'll wait and see what our partners in the EU come back and say."
He said it is "clear" there is now a "building majority" supportive of the plan in Parliament.