EU summit: Theresa May's Russia mission faces Brexit test

Guess what? The prime minister's priority in Brussels tonight won't be Brexit.

Yes, you read that right, top of Theresa May's list at the EU summit won't be giving the long-running talks a shove forward.

The deal over the transition period - the buffer zone between Brexit and the ending of all ties - only needs to be rubber stamped on Friday.

Of course, there are many more tangles to be sorted in the coming months. But tonight, the prime minister's main goal is to try to stiffen up the EU's response to the threat from Russia.

• May to warn EU leaders of Russian threat

At home, Theresa May has taken a firm rhetorical tone, in response to the nerve agent attack in Salisbury.

What the government hopes for in the next 24 hours though, is that the other EU nations are willing to come alongside in the same way.

The US, UK, France and Germany signed up to a very strong and uncompromising statement last week.

But the prime minister will tonight try to create a similarly strong and united front among the other 27 EU member states.

In extremely blunt language UK government officials have been briefing that Russia is a "strategic enemy" of Europe.

Theresa May will tell her counterparts that it is a risk to all. Number 10 wants a robust statement from everyone in response, a show of unity, and by implication, other countries to look to increase the pressure on Vladimir Putin.

She might not get her way, however. EU countries may share the UK's security concerns about Russia.

But member states like Greece and Hungary have their own reasons for concerns about taking a more hostile approach.

Can the prime minister get consensus tonight, even persuade other countries to start taking similar action against Russia?

It would never have been a straightforward quest to get more than two dozen countries into the same position.

But with one foot out of the door, does the UK's foreign policy influence have the same stretch?

This is one of the first tests of whether Brexit is harming Britain's powers of persuasion.

Will the rest of the EU see Theresa May tonight as the close friend who can hold the room, or with a year until exit, has she just become the awkward neighbour?