Jeremy Corbyn was laughed down by Tory MPs in Parliament, after claiming Boris Johnson’s Brexit deal would lead to "maggots in orange juice and rat hairs in paprika".
The Labour leader said a post-Brexit US trade would force the UK to slash food standards as he confirmed his party would not back the Prime Minister's deal.
Conservative MPs jeered and heckled as Mr Corbyn addressed the Commons.
He said: "The choice we now face is between keeping the highest environmental and food standards in order to get a future trade deal with the European Union or slashing food standards to match those of the United States where there are so-called acceptable levels of rat hairs in paprika, maggots in orange juice."
He insisted his warning was not a "piece of imagination" but "absolutely" the reality.
Mr Corbyn went on to label the Government's handling of Brexit a "national embarrassment", as he said his party "recognises the clear message" from voters at the election but confirmed Labour would not support the Withdrawal Agreement.
He said the Prime Minister's Brexit deal is "terrible", adding: "Labour will not support this Bill as we remain certain there is a better and fairer way for this country to leave the European Union.
"One which would not risk ripping our communities apart, selling out our public services or sacrificing hundreds of thousands of jobs in the process.
"This deal is a road map for the reckless direction in which the Government and our Prime Minister are determined to take our country."
Mr Corbyn made the claims as Mr Johnson urged MPs to "come together" and back his deal, so the UK could leave the EU by the end of January.
The Prime Minister said after years of division, it was time to "reunite our country" and "begin the healing".
He called for people to "discard the old labels of Leave and Remain" which have dominated since the 2016 referendum, and "finally get Brexit done".
It was approved by an overwhelming majority.
