British Prime Minister Boris Johnson would walk away from trade talks with the European Union if no progress was made by June, the British government warned in its negotiating mandate, published on Thursday.

London said it expected to see a "broad outline of the agreement" in four months, failing which Britain would be compelled to initiate preparations for a sharp break from the 27-nation bloc. Talks are due to start in Brussels on Monday.

"At the end of the transition period on the 31st of December, the United Kingdom will fully recover its economic and political independence," cabinet office minister Michael Gove told parliament as he unveiled the mandate.

"We want the best possible trading relationship with the EU, but in pursuit of a deal we will not trade away our sovereignty."

The UK officially left the EU last month and has until the end of 2020 to ink a trade deal and a host of other agreements to replace more than 40 years of almost identical political and economic ties.

The Withdrawal Agreement allows for the transition period to be extended by another 24 months but Johnson's Conservative cabinet insisted that the UK will exit EU structures, like the single market, as of 1 January, 2021.

Both sides are keen to arrive at a deal by the end of the year but have diverging perceptions on a number of subjects including tariffs, mobility, fisheries, law, environmental protections and state aid.

Their contrasting positions on what constitutes fair competition and a level playing field have belied expectations of smooth progress when the interlocutors meet in the Belgian capital.

Britain's negotiating mandate insists that "we will not agree to any obligations for our laws to be aligned with the EU's, or for the EU's institutions, including the Court of Justice, to have any jurisdiction in the U.K."

For instance, the British government's 30-page mandate seeks to have a trading relationship similar to what the EU has with Canada, South Korea and Japan.

In the event of a deadlock on a comprehensive deal, the UK would rely to the World Trade Organisation rules under an arrangement with the EU similar to Australia's.

Britain's blunt threat of no deal has not come as a surprise to Brussels which earlier accused Johnson of trying to dilute commitments enshrined in the divorce deal.

The EU's chief negotiator Michel Barnier said that the bloc had taken "note"of the mandate.

"We will stick to all our prior commitments in the political declaration," he tweeted.

"We want an ambitious and fair partnership with the UK in the future."

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