Carwyn has no cards to play over Brexit.

The UK Prime Minister's called  "grown up approach" to relationship with the devolved legislatures seems to floundered already

Welsh First Minister Carwyn Jones urged the UK Government to put meat “on the bones” of Brexit after leaving talks with Theresa May and the First Ministers of Scotland and Northern Ireland.

The Welsh Labour leader warned that Downing St talks had left them with “no more certainty as to where the UK Government is going”.

Scottish First Minister Nicola Sturgeon expressed frustration about the lack of clarity.

She said:

 “I don’t know any more now about the UK Government’s approach to the EU negotiations than I did before I went in to the meeting.
"I can’t speak for the other devolved administrations but I think there was a degree of frustration shared by all of us about that.”

Ms Sturgeon has said she will bring forward proposals for a "flexible Brexit" that would keep the Scotland in the single market even if the rest of the UK was not.

She added:

 "We have still got a lot of work to do, and I think it is incumbent on the UK government to inform that work by being much more open about what they are trying to achieve.
"I am determined, for my part, to do everything I can to work within this process as far as I can to protect Scotland's interests.
"My frustration is that I am hearing warm words from the UK government, but not yet seeing those warm words backed up by substance or action."

And she told the BBC she was not "bluffing" about the possibility of a second independence referendum, adding: 

"If all we get from the UK government is the door getting closed in our face, then I am absolutely determined that Scotland shouldn't be taken off that hard Brexit cliff edge without at least having the opportunity to choose a better future."

of course Carwyn  unlike Nicola has no cards to play . As John Dixon at Borthlas puts out.

"....Despite the Prime Minister’s statement that Carwyn Jones will have a direct line to David Davis to express his views, ‘expressing his views’ is all he will be allowed to do – and, of course, take his fair share of the blame for having been party to a process which will not deliver what he wants. Of course, if Wales were an independent country, then he really would have a veto over deals affecting us. But he doesn’t want that – he just wants to be able to stamp his feet and have an occasional tantrum. And then wonder why Wales’ voice is being ignored".

The Government "grown up approach" seems to resemble a Academic Governing Body" that allows representatives of the Student Body to attend meetings, and allow them to speak but do not alow them to put forward or amend motions, and they are crucially not allowed to vote,

Carwyn tried to puff up his position however, saying  expects the Assembly to hold votes before the triggering of the two-year exit process and also on the final deal.

When asked if votes in the devolved legislatures amounted to a veto on the process, he said: 

“Well, that’s the risk.

"Does the UK really want to go into negotiations in March with one or some of the devolved adminstrations actively criticising their position?“That doesn’t make sense. I’m not going to start on that basis.“I’m not here to try to be disruptive. I want to get to a position where we have an agreed position but we’re a long way from that yet.”

But Carwyn knows that not only did Wales vote for Brexit, he can't  threaten to seek an alternative strategy including the threat of Independence and/or Wales attempting its own deals with the EU in seeking the single market.

Even Northern Ireland despite its Unionist majority  do not want a Hard Boarder with the rest of Ireland and some may be considering the unthinkable that their future may be better served  in partnership with the rest of the Island and the European Union rather than a Hard Brexit which would cut them off from markets in the South and the rest of Europe.

Carwyn may think that pictures of him entering Number Ten, means that he will be seen as "a player",

But in reality he has no real voice, because he's not prepared make a case for Wales and back this with if not threats to the Union at least promises he will seek an alternative, to Wales' joining England  in being the first Lemmings to jump off the cliff,