Brexit: Welsh Government told not to undermine talks
Leaders of the UK's devolved governments must not "undermine" Brexit negotiations, Downing Street has said.
Theresa May has offered the Welsh Government a formal seat in talks to shape the UK's EU exit strategy.
But First Minister Carwyn Jones said there was "certainly a great deal of uncertainty" about the UK's position.
The joint ministerial council (JMC), which includes Mr Jones and the prime minister, met for the first time since 2014 on Monday.
Prime Minister Theresa May said it was "imperative" Wales helped make Brexit discussions work.
But Mrs May's official spokeswoman said: "We have been very clear that we should be working together to secure the best possible deal for the whole country.
"We expect representatives of the devolved administrations to act in that way and to in no way undermine the UK's position."
The prime minister offered the leaders a "direct line" to Brexit Secretary David Davis during the discussions.
Following the meeting, Downing Street said that a new cross-nations forum on the talks to leave the EU would be set up, chaired by the Brexit secretary.
Plans are to be drawn up to integrate it with the "wider process of exiting the EU", with the first meeting set for November ahead of the triggering of Article 50 by the end of March.
The prime minister said she wanted the JMC to meet more regularly and would set up another session early next year.
Further work is to take place on putting the committee on a new formal footing with "guaranteed" annual meetings.
Mrs May said: "The country is facing a negotiation of tremendous importance and it is imperative that the devolved administrations play their part in making it work."
Welsh Secretary Alun Cairns also attended the meeting at Downing Street, alongside Scottish First Minister Nicola Sturgeon and the First Minister and Deputy First Minister of Northern Ireland, Arlene Foster and Martin McGuinness.
Speaking after the meeting, Mr Jones said: "We don't know what the meat on the bones will be or indeed the general principles for the negotiation."
But he welcomed the "work programme" and said that it was "absolutely essential" to hold these meetings more frequently and ensure that the nations' voices were heard.
In a statement, Mr Jones said the starting point for Brexit negotiations must be "full and unfettered access to the single market".
He also welcomed agreement by the UK government for the JMC to meet more frequently.
But Welsh Secretary Alun Cairns said the UK government would have been criticised for not engaging with devolved governments if it had stated a certain position on Brexit,
On Saturday, the prime minister said she wanted the meeting to be the "start of a new grown-up relationship between the devolved administrations and the UK government".
Mr Cairns said Mrs May had set a "clear framework" for Wales to be at the centre of any Brexit negotiations.
But Mr Jones warned there needed to be a clear agreement between the different administrations before the UK pushed ahead with a deal to leave the EU.
Meanwhile, Plaid Cymru urged the first minister to prioritise protecting Wales' membership of the single market during the meeting of the JMC.
Shadow secretary for external affairs, Steffan Lewis, said: "Unless the first minister shows strong leadership and outline decisive demands - factors which have been absent from his response to the referendum result so far - there is a danger that Wales will become a bystander to Brexit".