The Government is currently attempting to negotiate a new trade deal with Brussels. This would come into effect when the Brexit transition period finishes at the end of the year.
However talks remain deadlocked over European access to British fishing waters and the EU’s demand for a regulatory ‘level playing field’.
Speaking to The Telegraph a source close to the European Research Group (ERG), a Eurosceptic group of Tory backbenchers, delivered a warning to Mr Johnson.
They said ERG members could vote against the trade deal in the House of Commons unless their red lines are respected.
The source commented: “For Brexiteers, the overwhelmingly important issue is UK sovereignty.
“If that is not preserved in the final agreement, I have no doubt we will vote against the treaty in whatever vote is called.”
Whilst Britain formally left the EU at the end of January it remains in a Brexit transition period until the end of this year.
During the time the UK retains membership of the European single market, but must continue paying into the EU budget and implementing Brussels legislation.
If no new deal is agreed Britain and the EU will trade on World Trade Organisation (WTO) terms, with tariffs on many products.
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If the ERG does oppose a trade deal agreed by Mr Johnson he may need the help of Labour MPs to get it through Parliament.
Sir Keir Starmer has previously indicated he is keen for a new trade agreement to be reached.
Brexit Party leader Nigel Farage has warned “Brexit is now in peril” amidst rumours of a compromise.
Earlier this month he announced his faction will be rebranded as the Reform Party, and will campaign against coronavirus lockdowns and any concessions of sovereignty to Brussels.
According to The Telegraph over 3,000 people have already put their names forward to stand for the Reform Party in next May’s local elections.
Speaking to the paper a source said: “We are going to be standing in London Assembly, Scotland, Wales, all of the police and crime commissioners, a big focus on law and order.
“There are 5,000 local council seats up for grabs, and we are going to be targeting as many of those as possible.”
On Wednesday the Office for Budget Responsibility predicted a hard Brexit at the end of the year with no trade deal will knock two percent off the UK’s GDP in 2021.
If this happens it predicts GDP would remain 1.5 percent lower in five years time.
Michael Gove, a senior Cabinet Minister, has warned “not everything will be alright on the night” even if a deal is agreed and predicts several weeks of disruption before things “settle to a new normal”.