The European Parliament on Wednesday overwhelmingly ratified the EU's post-Brexit trade deal with Britain, but promised to keep a close eye on London with cross-channel tensions still high.

The vote approved the bare bones trade deal with the bloc's third-biggest trading partner that was sealed on Christmas Eve after nine months of tough negotiations.

The agreement provides the framework for London's new relationship with the 27-member union, five years after British voters shocked the world by voting to end its 47-year membership.

In the final tally, 660 MEPs voted in favour of the trade deal, five against with 32 abstentions, results released Wednesday showed.

"The European Parliament voted on the most far reaching agreement the EU has ever reached with a third country," the president of the assembly, David Sassoli, said. 

"This can form the foundation on which we build a new forward-looking EU-UK relationship," he said, warning that MEPs would monitor the implementation of the deal and "not accept any backsliding from the UK government." 

British Prime Minister Boris Johnson hailed the "final step in a long journey" that brought "stability to our new relationship with the EU as vital trading partners, close allies and sovereign equals." 

"Now is the time to look forward to the future and to building a more Global Britain," he added.

The vote comes amid multiple feuds over the UK's implementation of Brexit agreements and angry finger-pointing about the supply of the Covid-19 vaccine from AstraZeneca.

Deepening tensions further, France has threatened to block UK financial firms doing business in the EU if the London does not respect its commitments on fishing, a key part of the deal.

EU chief Ursula von der Leyen "warmly welcomed" the greenlight, but in a final debate in parliament on Tuesday, assured MEPs that the agreement had "real teeth" and had ways to keep the UK in check.

"Let me be very clear: We do not want to have to use these tools, but we will not hesitate to use them if necessary."

Britain's Brexit minister David Frost said he "hugely" welcomed the vote to approve the deal he helped negotiate during months of fraught talks with EU counterpart Michel Barnier.  

"Hope we can now begin a new chapter together as Europeans, characterised by friendly cooperation between sovereign equals," Frost wrote on Twitter.