Will Brussels back down on the backstop? Don't hold your breath

"As President Juncker said, the deal is the best and only deal possible, our position has therefore not changed."

That was the emphatic statement from Mina Andreeva, the spokeswoman for the EU Commission, at the daily briefing in Brussels today.

An hour or so earlier, Simon Coveney, Ireland's Deputy PM, arriving for a meeting of Foreign Ministers at the EU Council, said: "We are saying the deal that is there, the deal between the UK and the EU, isn't going to change, particularly the legal language of the withdrawal treaty."

Clearly both are signposting that the only room for making concessions to the Brexit package deal, at this stage, is to tinker with the Political Declaration. That's the 26-page outline of a future trade agreement with the EU.

• Theresa May tries to call off crunch Commons Brexit vote

• Can the PM survive the failure of her Brexit plan?

• UK can unilaterally halt Brexit, European Court rules

• Twelve key Brexit buzzwords explained

There could also be additional written assurances, perhaps relating to the backstop, added to the Withdrawal Agreement, as there was on the subject of Gibraltar the day before November's EU summit.

Neither of those are legally binding options though and the Democratic Unionist Party, who've been supporting Theresa May in power, have signalled just as clearly that changing anything that isn't legally binding just won't placate their fears and objections.

Spotted arriving in Brussels this morning was Olly Robbins, the UK's negotiator. A photo of him walking out of the Eurostar terminal shows him carrying a large rucksack. He looks like he's in for the long-haul and dressed suitably for a last push towards the summit being held in Brussels on Thursday.

Yet, it's very difficult to know what Theresa May, and Olly Robbins, think they can change within the terms of the Brexit package, as it stands, that could possibly ease its course through the Commons.