Brexit won't be delayed by the successful legal challenge that has been mounted against the Government, Theresa May is to say.
The ruling won't stop the Government from triggering Article 50 by March 2017 and leaving the EU two years later, according to a spokesperson.
Mrs May is to speak with other European leaders and tell them that there will be no delay to the plans, despite the extraoridnary ruling. The Prime Minister is set speak by phone with European Commission president Jean-Claude Juncker on Friday, and Downing Street indicated that she is also hoping to talk with European Council president Donald Tusk and leaders of some of the other 27 member states.
The High Court's ruling that the Government should seek Parliament's approval before triggering Article 50 withdrawal negotiations was welcomed by some in Brussels.
The European Parliament's Brexit negotiator, Belgian MEP Guy Verhofstadt, said it was "important the UK Parliament is closely involved in Brexit negotiations, as is already the case for the European Parliament".
Mrs May's official spokeswoman said the Prime Minister would use the calls to European leaders to explain Britain's position that "we are continuing with our plans, that the timetable she set out at the European Council is the timetable that we are sticking to".
The spokeswoman added: "She will set out what the process is, which is that we are appealing and that we are carrying ahead and sticking to the timetable we have set out. This judgment is not going to derail that."
She added: "From the outset of taking office, the PM has sought to engage with other European leaders, to have that open dialogue. She talks to them regularly."
Mr Juncker's spokesman told reporters in Brussels that the phone call was taking place at the request of the Prime Minister.
Asked about the High Court ruling, the spokesman said: "We will not comment on issues that pertain to the internal legal and constitutional order of our member states."
He added: "The Article 50 procedure, as set out in the treaty, requires the consent of the European Parliament for any Article 50 agreement."
The spokesman said all the other members of the EU would like to see a "swift" notification of Article 50 to begin the Brexit process.
"It was not the commission that asked for a swift notification under Article 50," he said.
"If memory doesn't fail me, it was all 27 member states that asked for it at the highest level."
The spokesman said it was not a matter for the European Commission to speculate on the impact of the High Court ruling on the timing of Article 50 being triggered.
Additional reporting by Press Association
