British Transport Secretary Chris Grayling has sought to downplay hard border fears for Ireland before failing to guarantee trade barriers will not exist.
The Cabinet minister said the UK is introducing measures to ensure there is "no issue our way" but acknowledged the Irish government could "put barriers in the way of trade".
He added he "cannot for a moment believe" the Irish government will put administrative systems in place which are not introduced by the UK.
Mr Grayling's stated confidence appeared to do little to ease opposition concerns as MPs debated the Haulage Permits and Trailer Registration Bill.
Shadow transport secretary Andy McDonald said there was an increasing frustration and anger among the freight and logistics industry at the Government's "cavalier it'll be alright on the night" approach.
He added: "There is no evidence that economic self-interest will prevail."
The Bill is viewed as the first major piece of Brexit contingency legislation and contains powers to allow the Government to create a travel permit scheme to enable commercial cross-border transport to continue if no agreement was reached with the EU.
It would also establish a trailer registration scheme to ensure UK operators could continue to use roads in those EU countries that required it.
Speaking at second reading, Mr Grayling said the UK is committed to maintaining the existing "liberalised" access for haulage.
He claimed this is the "by far the most probable" result of Brexit talks although noted it would be "irresponsible" not to plan for all eventualities.
Mr Grayling also said road haulage and trailer registration are devolved in Northern Ireland.
He added: "With regards the Republic of Ireland and Northern Ireland, this Bill supports the commitment made in December 2017 to avoid a hard land border.
"It's an enabling Bill. The Government will preserve the constitutional and economic integrity of the United Kingdom.
"The Government is committed to ensuring trade and every day movements over the land border continue as they do now, and the Bill does not create a permit regime in relation to the Republic and Northern Ireland, nor does it create a hard border between them.
"It means trailers travelling only between UK and Ireland will not need to be registered."
DUP Brexit spokesman Sammy Wilson questioned if there will need to be a separate agreement between the UK and Irish governments over the need for permits or a separate arrangement for people taking lorries across the border.
Mr Grayling replied: "I can't speak for the Irish government. What we're doing is putting in place the mechanism which ensures there's no issue our way.
"The Irish government of course is perfectly able, as any other government is, to put barriers in the way of trade. We won't do that. We won't create a regime that effects those travelling into the Republic of Ireland, through the Republic of Ireland to the United Kingdom.
"I can't give guarantees on behalf of the Republic of Ireland but I cannot for a moment believe that they will want to put in place administrative systems which we don't put in place."
Mr Grayling added he is entirely confident a sensible place will be reached between the two parties by the end of the negotiations.
For Labour, Mr McDonald said: "(Mr Grayling) has come to the despatch box and said he doesn't speak for the other 27 governments.
"I sometimes wonder whether he speaks for the one he's got right in front of him because a damaged and disrupted logistics sector will result in a damaged and disrupted British economy."
He added the Government has made "a complete and utter dog's breakfast" of contingency planning for the M20, which is the route to Dover.
Mr McDonald went on: "If this Government can't successfully plan how to build a lorry park in Kent, how do they expect anyone to believe it is capable of introducing an alternative haulage permits scheme?"
SNP transport spokesman Alan Brown said a number of uncertainties surrounded the legislation, such as what additional checks would be required as well as questions about the Irish border.
He said: "It would seem to me there are still a lot of known unknowns with regards to this Bill."