The European Union has warned the UK it will "not be shy" in taking legal action against any "violations" of the Brexit Withdrawal Agreement, setting the stage for a brutal showdown ahead of the UK's full exit from the bloc at the end of the year. 

"The Withdrawal Agreement is to be implemented, not to be renegotiated, let alone unilaterally changed, disregarded or disapplied," European Commission Vice President Maros Sefcovic told reporters after a meeting with the UK's Cabinet Office Minister Michael Gove on Monday.

Brussels has given Downing Street until the end of September to withdraw the controversial Internal Market Bill or face the consequences. 

The bill, which was introduced by UK Prime Minister Boris Johnson earlier this month and is currently making its way through the House of Commons, would override parts of the Brexit divorce deal relating to Northern Ireland. 

The EU says this is a breach of international law and threatens the Good Friday Agreement, which brought decades of bloody unrest to an end on the island of Ireland. 

On Monday, Gove doubled-down on the legislation, saying the clauses pertaining to the Northern Ireland protocol "will remain in that bill" and reiterated Johnson's assertion that the bill serves as a "safety net" if talks on a post-Brexit trade deal fail.

"We want to reach agreement in the joint committee, we want to make sure that the position of Northern Ireland is secure in the UK, we want to make sure the Withdrawal Agreement is implemented in full," Gove said in a televised statement after his meeting with Sefcovic. "But those clauses are there and they are in legislation supported by the House of Commons as a safety net if need be ... And those clauses will remain in that bill."

UK bill throws long shadow over post-Brexit trade negotiations

Brussels says it will not halt Brexit talks over the disputed bill, but the legislation throws a long shadow over what are already intense trade negotiations. The last scheduled round of talks ahead of an October deadline kick-off in earnest in Brussels on Tuesday. 

Both sides admit they remain far apart on several issues, including fishing rights to British waters and a "level playing field" for EU and UK companies, especially when it comes to state aid.

The two chief negotiators, Michel Barnier and David Frost, will meet in Brussels on Friday. If progress is made, both sides will enter a two-week period of intense negotiations ahead of an EU leaders' summit on 15 and 16 October. 

The UK's Johnson has threatened to walk away from talks if an agreement can't be reached by then. Brussels has given a bit more wiggle room, stretching the deadline until the end of the month. Regardless of the deadline, one thing is clear: time is running dangerously short for a deal to be ratified and in place for 1 January.