The EU politician blasted the United Kingdom delaying Brexit talks, choosing to focus on "procedure" rather than the heart of the withdrawal from Brussels.
Ms in't Veld said: "I really hope that everybody will climb down from their high horse and start to seriously negotiate substance rather than procedures.
"This is the way it’s laid down in the treaties. The treaty has been modified as recently as 10 years ago and the UK Government at the time agreed to the treaty."
Ms in't Velt attacked the UK for questioning the Brexit system pursued in Brussels
Speaking to BBC World at One, she said Britain was challenging the Brexit mechanism despite having agreed to the rules when the withdrawal option was first introduced with the Treaty of Lisbon.
She said: "It’s a bit frustrating to start challenging the rules that the UK itself has agreed to. I’m getting a little bit exasperated because it seems that for months and months now, all we are doing is discussing the rules of the game."
Before 2007 EU law did not include provisions that allowed member states to voluntarily leave the institution and to this day the UK is the only country to have ever triggered the exit process.
Tension has been growing between Brussels and the UK after yet another fruitless round of Brexit talks in Brussels.
It comes as Chancellor Philip Hammond urged his colleagues to stop bickering and focus on the Brexit talks deadlock.
Mr Hammond said: “My message is this: I understand that passions are high and I understand that people have very strong views about this but we're all going to the same place, we all have the same agenda.
"The enemy, the opponents are out there, they're on the other side of the negotiating table. Those are the people we have to negotiate with, negotiate hard to get the very best deal for Britain."
The Chancellor's outburst will come as a surprise to many who considered him one of the more moderate members of Theresa May's Cabinet and follows rumours that he would prefer to see a 'soft Brexit' deal, retaining as many EU ties as possible.
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