The tone on both sides of the English Channel has been alarming over the last few months, casting a shadow over the start of the U.K.'s departure from the European Union, an European lawmaker told CNBC.
"The first thing to watch is the tone," Seb Dance, a member of the European Parliament for the Labour Party, told CNBC on Wednesday. "The tone (between the U.K. and the EU) has been dreadful so far."
As Prime Minister Theresa May prepares to trigger Article 50 of the Lisbon Treaty at lunchtime Wednesday, Brussels and London are worlds apart at the start of this process.
The U.K.'s intention to exit the single market was a game-changing moment for the EU, Dance said. Until Prime Minister May's speech in January outlining her vision for Brexit, there was "a lot of good will" in Brussels, but that changed once she promised to break free from the common market – which allows businesses to trade freely within the EU borders.
But there are other outstanding issues clouding the start of the process. It is not yet clear how the negotiations will unfold but whereas the EU wants to discuss how the U.K. is leaving before agreeing on a new trade deal, the U.K. government wants to discuss every single issue within the two-year deadline.
Other differences include Britain's liabilities and how much it is willing to pay the EU before leaving. Brussels said this could mount to 60 billion euros ($65 billion), but the British government has dismissed the figure.