Boris Johnson has been warned against taking the people of Northern Ireland for "fools", as he attempted to convince MPs over his Brexit deal.
Independent Lady Sylvia Hermon (North Down) warned the British prime minister that the European Union (Withdrawal Agreement) Bill fails to explain the new consent process for Northern Ireland in the draft deal.
DUP MPs also lined up to express concerns about the compatibility of the deal with the Good Friday Agreement, which requires cross-community decision-making.
DUP MP Emma Little Pengelly (Belfast South) said: "I have serious concerns that there has been some mistake in relation to the printing of the Withdrawal Agreement."
She told the Commons there had been reference in the prime minister's speech to "clauses and provisions" which would see provisions for Northern Ireland "disappear" once a free-trade deal had been signed.
She said: "I cannot find those clauses. I took the opportunity during the leader of the opposition's speech to look at it again, I cannot find those clauses within my copy."
Commons Speaker John Bercow said she should make a point of intervening when the contents of the Bill are discussed.
Labour MP Catherine McKinnell (Newcastle Upon Tyne North) said: "I too noted that the prime minister referred to checks and declarations on GB Northern Irish goods being transitory and melting away unless a majority of Northern Ireland choose to retain them.
"And I also share concerns that that is not, in fact, correct and, perhaps, there has been some confusion between the future decisions relating to a single market, and being in a customs union."
Assembly consent for extending an initial four-year period for the post-Brexit arrangements, which include the creation of an all-island regulatory zone on goods, would be done on the basis of a simple Stormont majority.
Speaking during a debate on the Bill, Lady Hermon said: "I say very clearly to the prime minister, do not take the people of Northern Ireland for fools - we are not fools. The prime minister needs to explain in detail how his new consent process operates."
Mr Johnson said the process is detailed in the unilateral declaration made between the UK and the Republic.
He added there are a "small minority of economic arrangements" in Northern Ireland which remain in alignment with the EU for four years unless and until a majority vote of the Stormont Assembly elects to remain in alignment.
DUP Westminster leader Nigel Dodds said: "It is quite clear that whatever you say about Northern Ireland being in the UK customs union, de facto the European Union customs code applies in Northern Ireland if the protocol comes into place which requires exit declarations from Northern Ireland."
Mr Johnson replied: "There are no checks GB/NI. There will be some light-touch measures to ensure there is no illegal trade. Illegal trade in endangered animal species and banned firearms, which I think you would agree was sensible."
He added: "Even these measures evaporate and are terminated automatically, they automatically dissolve, unless a majority of the Northern Irish Assembly in Stormont votes to keep them."
DUP MP Sammy Wilson (East Antrim) also said: "The simple plank, Prime Minister, for the mechanisms ensuring both communities are protected in the Belfast Agreement is, and I state from the agreement itself, 'to ensure that all sections of the community can participate and work together, and that all sections are protected, arrangements to ensure key decisions are taken on a cross-community basis'."
He questioned how this complies with the terms of the prime minister's agreement and his earlier comments that decisions are made "on a majority basis".
Mr Johnson replied: "It is the salient feature of these arrangements, that they evaporate, they disintegrate, they vanish, unless a majority of the Northern Ireland assembly elects to keep them."
Simon Hoare, Conservative chairman of the Northern Ireland select committee, said no border communities in Northern Ireland are "fearful of a resurrection of violence and bloodshed and hatred" thanks to the prime minister's deal.
He added: "Trying to square the difficult circle of delivering Brexit, under the umbrella of the Good Friday Agreement and maintaining peace on the island of Ireland was always going to be a big ask.
"Not everybody will be happy with what the Prime Minister is bringing forward, but all communities should be happy that nobody is talking about 'a coach and horses being driven through the Good Friday Agreement'.
"And there are no communities, particularly at the border, who are now fearful of a resurrection of violence and bloodshed and hatred.
"The prime minister is to be congratulated."
But Labour leader Jeremy Corbyn said: "This Bill confirms Northern Ireland is really in the customs union of the EU and goods will be subjected to tariffs."
