Brexit chief negotiator Michel Barnier this morning described the UK's decision to formally file a request to leave the EU as "day one of a very difficult road" for both parties.

Commissioner Barnier made these remarks during the opening exchanges of a meeting at Castille with Prime Minister Joseph Muscat, who was accompanied by EU Affairs Minister Louis Grech.

The meeting, which was only open to the media for the first few minutes, took place a few hours before EU Council President Donald Tusk was set to receive the UK's formal request to trigger Article 50 of the Lisbon Treaty, kicking off the two-year exit negotiations.

READ: Britain set to trigger Article 50 today

Describing it as a "key moment" for the EU, Commissioner Barnier spoke on the need to reach a "fair agreement" not only on the Brexit issue but also for the long-term future of the EU itself.

On his part, Dr Muscat reiterated his view that any fair deal had to nevertheless be inferior to membership. He said that once the process would be officially triggered, Malta, as EU Council president, would be delivering the official Brexit negotiations guidelines to Commissioner Barnier within 48 hours.

Dr Muscat pointed out that he did not envisage having 27 separate negotiations going on, nor for the EU Council Presidency to hold separate talks. That responsibility will be shouldered byCommissioner Barnier alone on behalf of the EU, he added.

"We will rely on your good judgment This is a sad day for the EU," the Prime Minister said.

On the other hand, Dr Muscat expressed his confidence that the EU would move ahead.

Asked for his reaction following the meeting, Mr Barnier said that it had been “a very good meeting”. He also heaped praise on the Maltese EU Council Presidency.