Sammy Wilson, Brexit spokesman for the Democratic Unionist Party's 10 MPs in Westminster, | Leon Neal/AFP via Getty Images DUP lawmaker slams ‘nutcase’ Irish prime minister Northern Irish party’s Brexit spokesman brands Leo Varadkar ‘naive’ and ‘arrogant.’

LONDON — Irish Prime Minister Leo Varadkar was accused on Wednesday of being naive, inexperienced and arrogant for siding with European Union negotiators in Brexit talks.

Sammy Wilson, Brexit spokesman for the Democratic Unionist Party's 10 MPs in Westminster, branded the prime minister a "nutcase" and claimed there had been a change of tone from Dublin since Varadkar took office last June.

Wilson said the U.K. government needed to find a way of either "cajoling or enticing" the Irish government into taking the "natural position" to "cut [the U.K.] some slack," warning that siding with "hard-line EU negotiators" could destroy the Irish economy.

His comments came after Varadkar said in a speech to the European Parliament in Strasbourg on Wednesday that the U.K. could not “backslide” on commitments on the Irish border made in the first phase of Brexit negotiations.

But Wilson, who attends some U.K. government meetings as part of his party's arrangement with the Conservatives, said: "It was always our view at the very start of this process that the biggest ally we would have when it came to negotiating with the European Union was Dublin, and indeed that always was the impression we got when Enda Kenny [the former Irish prime minister] was in power, but since this nutcase Varadkar has taken over that things have all changed."

He blamed this on "naivety, inexperience, arrogance on his part."