European Commission President Jean-Claude Juncker told British Prime Minister Theresa May on Wednesday that the bloc's Brexit divorce deal with London cannot be renegotiated, CNBC reported.

"The Withdrawal Agreement remains the best and only deal possible," Juncker told the European Parliament. "The debates and votes in the House of Commons yesterday will not change that. The Withdrawal Agreement will not be renegotiated."

"Ireland's border is EU's border and is our joint priority," Juncker said of the contentious issue of the Brexit border backstop. "Yesterday's vote has further increased the risk of a disorderly Brexit."

But Junker also said he was an optimist and hence believed "there can and will be agreement with UK."