Reform UK has been told to "get a new gig" amid a row with Labour over its European Union reset deal.
Sir Keir Starmer secured new arrangements with Brussels on a number of issues earlier this year, including defence and migration.
Britain and the EU also reached a 12-year agreement on fishing.
But the deal has been widely panned by Brexiteers - who have dubbed it a "surrender".
On Sunday, a leading think tank warned that the accord would do almost nothing to boost trade - and urged policymakers to look inwards to the UK rather than to Europe to boost growth.
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While in the past, Nigel Farage has suggested it could mean "the end" of Britain’s fishing industry, and ex-Home Secretary Suella Braverman has labelled it a "betrayal of democracy" and "an insult" to 17.4 million Brexit voters.
Now, a Cabinet Office source has told GB News that Reform and the Conservatives should "get a new gig", adding that it is "not 2016 anymore".
"Very bitter, very sad, from Tories and Nigel Farage," the source said.
"They want to rip up a deal that benefits jobs and bills in the United Kingdom, and all because they are incapable of bringing themselves to have any relationship with Europe.
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The Government has said the deal would almost £9billion into Britain's economy
|GETTY
“Maybe it is a lack of aspiration thing. Maybe they're just cranks.
“Cooked aura farming. It’s not 2016 anymore. Get a new gig.”
The Government previously said that it believes the agreement could lower food prices and increase choice on supermarket shelves.
Some foods that were previously prevented from being sold in the EU since Brexit have been returned to European shelves, including British sausages and Aberdeen Angus burgers.
Nigel Farage has suggested the deal could mean 'the end' of Britain’s fishing industry
|PA
Speaking at the UK-EU Summit at Lancaster House earlier this year, the Prime Minister said: "It’s time to look forward.
"To move on from the stale old debates and political fights to find common sense, practical solutions which get the best for the British people.
"We’re ready to work with partners if it means we can improve people’s lives here at home.
"So that’s what this deal is all about – facing out into the world once again, in the great tradition of this nation.
"Building the relationships we choose, with the partners we choose, and closing deals in the national interest. Because that is what independent, sovereign nations do."
Labour also said the deal would almost £9billion into Britain's economy.
"We have reset our relations with the EU - our closest partner and biggest market - to support British businesses, back British jobs, and put more money in people’s pockets," a Government spokesman said.
"Our agreement will help make food cheaper, slash red tape, open up access to the EU market and add nearly £9billion to the UK economy."
A think tank has however claimed the EU reset deal will do almost nothing to boost trade, with businesses facing the possibility of higher costs.
"A ‘reset’ which focuses on a regulatory realignment with the EU may not be essential for the UK’s economic growth," the think tank said.
"Policymakers would be better looking to domestic economic reform [...] or trading opportunities beyond the EU."