The Brexit negotiations are poised to resume, but there are now two distinct and highly subjective realities: the world of the negotiating teams, and the paradigm of Tory politics.

If the process inches towards a successful outcome, it will only be through highly secretive negotiations in Brussels, accompanied by skillfully drafted statements, containing both coded references for the EU, and overt reassurances for Brexiteers.

Both are still, on the face of it, mutually incompatible.

Yet, so narrow is British Prime Minister Theresa May’s room for manoeuvre that this is the only path available.

The other element which is coming more sharply into focus is how the UK’s efforts to secure a temporary customs arrangement that would be UK-wide - and thus thwart a Northern Ireland-specific backstop - are bleeding uncomfortably into the future trade relationship.

While the temporary customs fix is attractive to London, it could trigger some very unpalatable truths relating to how much negotiating capital on the future trade deal the EU is prepared to give away, just because London wants a more politically convenient way of solving the Irish border problem in the immediate term.

It's understood Michel Barnier, the EU’s chief negotiator, drew member states’ attention to some of these very issues when he briefed them in Luxembourg on 16 October.

And one such issue is highly sensitive to the UK: fisheries (more of which later).

Despite all this there is (very) guarded optimism in Dublin that a deal is doable in the coming weeks.

"There are ingredients on the table where the British and the Task Force have to lock horns again," said an Irish source familiar with the negotiations, "to test if everything is as it appears. Then they’ll see if can they land on a version that they both agree on at negotiator level.

"My instinct tells me it’s doable. But we’ve been here before and it’s unravelled."

As always the process is hamstrung by what is happening within the UK parliament and cabinet.

Both teams of negotiators were close on the run up to last week’s European Council. However, a difficult cabinet meeting in the previous week, followed by another just before the summit, convinced Theresa May she did not have the political support to proceed.

Brexit Secretary Dominic Raab’s dash to Brussels the previous Sunday was more to inform Michel Barnier that the process had to wait due to cabinet opposition, rather than to overrule Olly Robbins, Theresa May’s chief negotiator, for going too far, as has been suggested.

That’s why the Prime Minister had little to say to EU leaders ahead of their 17 October dinner in Brussels (and why four of them could go drinking in the Grand Place later).

It’s also why there were no meetings of negotiators this week: the Prime Minister had to get through another (stormy) cabinet meeting on Tuesday, she had a potentially gruelling appearance before the 1922 Committee, and Philip Hammond will present the budget on Monday.

But British and EU Task Force officials have been in touch, and will seek to pick up the outlines of an agreement from where the talks left off.

The most important development is that the EU has shifted on London’s demand for a UK-wide customs backstop.

The so-called Temporary Customs Arrangement (TCA) was first produced in June as London’s alternative to the Northern Ireland-specific backstop.

It was almost immediately dismissed by Michel Barnier for three reasons: it would not solve the Irish border issue "in all circumstances" as it was only temporary; the Withdrawal Agreement was the wrong legal basis for what was really a future relationship issue; it would undermine the EU’s own customs and trading order.

London persisted, arguing that Paragraph 49 of last December’s Joint Report facilitated such an approach.

The backstop, after all, would see "the UK...maintain full alignment with those rules of the Internal Market and the Customs Union which, now or in the future, support North-South cooperation, the all-island economy and the protection of the 1998 Agreement."

Dublin and Brussels still dispute that interpretation. As such, the draft legal text produced last February spelled out in clear terms that the backstop was Northern Ireland-specific (indeed, the wording made clear Northern Ireland would remain in the EU’s customs territory in the event of the backstop taking effect).

The Task Force has since been re-drafting that text to make it less offensive to London and the DUP.

References to Northern Ireland remaining in the EU’s customs territory are said to have been removed, and it’s understood that commitments to the backstop being "superseded" if anything better came along have been reinforced.

But the text as it currently stands still foresees a Northern Ireland-specific backstop as the ultimate insurance policy. This would be underpinned by references in an annexe that, should the backstop take effect, the Union Customs Code (UCC) will apply in Northern Ireland.

London is still pushing back hard against that. One line of argument by British officials is that the backstop disproportionately favours only one strand of the Good Friday Agreement, ie North-South cooperation.

Indeed, it’s understood British officials have tried to dislodge the backstop from the Withdrawal Agreement altogether, in the hope it couple be shifted into the Political Declaration that will accompany the divorce treaty.

One suggestion is that London is trying to frame the TCA as being fundamentally about Northern Ireland, and so therefore is seeking to package the existing elements of the Irish Protocol about protecting the Good Friday Agreement into the TCA.

In that way, there would be a promise that this Customs Union caters to the specific needs of Northern Ireland.

That seems to be a non-starter, as it would remove the Northern Ireland-specific backstop from the Withdrawal Agreement, neutering its legal weight.

"There is no way in which this [temporary customs arrangement] will be a replacement for the backstop dealing with the island of Ireland situation which was agreed last December and repeated again in March," Ireland’s EU Commissioner Phil Hogan (above) told this week’s Brexit Republic Podcast on RTÉ.

"There will not be an opportunity for the EU side to agree that the backstop of December and March is kicked down the road into the future relationship."

It appears, however, that the EU has accepted the idea of a UK-wide customs backstop.

I understand the most recent draft of the text contains a prominent reference in the Irish Protocol to the effect that the EU will commit to negotiating an EU-UK customs union. While earlier suggestions located the promise in the non-binding preamble to the Protocol, it now seems that commitment will have legal weight as an article.

However, two well-placed sources insist this can only be negotiated as a separate treaty, even if the promise of it is contained in the Withdrawal Agreement.

This is why the UK has suggested extending the transition period.

If a separate treaty was going to be drawn up after 29 March - aside from the larger and wider future relationship negotiations - then a longer transition would be needed. Once the Withdrawal Agreement is concluded, it will be too late to extend the transition, so London has just a few months to apply for it.

It seems clear that this is where negotiators were landing before the talks froze on Sunday 14 October.

All of this was going on in the so-called "tunnel", the secretive space in which both teams were negotiating and from which precious few details have emerged ("what goes in the tunnel stays in the tunnel," as one diplomat advised).

So, when Theresa May told the House of Commons publicly on Monday that the EU was "actively working with us" on the UK-wide proposal, some EU officials were wondering if the code of the tunnel had been broken.

Equally, Irish officials looked carefully at the four demands the prime minister set out, to see if she was hardening, or softening her position.

These "four steps" are as follows:

A legally binding commitment to a "temporary UK-EU joint customs territory" (The Commission appears to be accepting this idea).

An extension to the transition "as an alternative to the backstop" (Not a runner, according to Dublin and Brussels)

Ensuring that if either the backstop or the extension were needed the UK could not be kept in them "indefinitely" (This is confusing, since she seemed to have said one was replacing the other).

Ensuring full continued access for Northern Ireland’s businesses to the whole of the UK internal market. (This is interesting, as there has never been any intention to inhibit goods flowing from Northern Ireland to the UK; the problem is goods flowing in the other direction. This the prime minister did not mention.)

Having said the transition was "an alternative to the backstop", Mrs May then said this in response to a question from Jeremy Corbyn: "Whatever future relationship we have," she told the Labour leader, "we do have to deal with the backstop issue.

"Without a backstop in the withdrawal agreement, there will be no withdrawal agreement. Without the withdrawal agreement, there will be no future relationship - nothing is agreed until everything is agreed - so it does not matter what future relationship we want, we still need to deal with this backstop issue."

One Irish source who followed proceedings reflected on the perils of interpretation: "There was a bit of reading between the lines and a bit of awareness of some of the things in the negotiations that you could see she was pointing to.

"At face value I think it was OK. The trouble is, if you chose to put on a different lens you might see things differently. People are accepting in good faith that some of the things she was saying she meant, in a way that is compatible with what we are hearing from the negotiating bubble."

Sources in Dublin believe there may be scope to bridge the gap between London’s insistence that a Northern Ireland-specific backstop is unacceptable, and Ireland’s insistence that it remain intact.

None of those ideas have yet been made public, and once negotiators return to the tunnel they will attempt to maintain secrecy.

However, the issues now being explored as we get to the end-zone point to further difficulties down the line.

First of all a temporary customs union is not magicked up overnight.

"It’s much more complicated than it sounds," says one source.

"It’s very complicated to work out all the details in a short period of time. These things need to be negotiated properly."

The second problem is political. The main off-the-shelf Customs Union the EU has at hand is the one with Turkey, agreed in 1995 (there are two others, with Andorra and San Marino, but these are not comparable for obvious reasons).

It has always been seen as disadvantageous to Ankara. It does not cover agriculture goods, and Turkish goods also require checks for regulatory compliance.

Turkey must also comply with other EU-third country trade deals, but not on a reciprocal basis.

In other words, under the EU-Canada deal (CETA), Canadian goods can circulate tariff- and quota-free in Turkey, but the same does not apply for Turkish goods destined for the Canadian market.

Would Brexiteers sign up to a situation where third country goods can flow freely into the UK without reciprocal access for UK goods?

It’s unlikely.

The EU will also want to know how a TCA will impinge on its existing free trade agreements and what it means for what officials call "the autonomy of decision-making" (ensuring that whatever is agreed between Brussels and London does not tie the EU’s hands in maintaining its own trade and customs arrangements).

Furthermore, it seems clear that the EU will only sign up to a TCA if it signposts the UK’s long term customs arrangement with Brussels.

London aspires to what it calls a Facilitated Customs Arrangement (FCA) taking over from the temporary customs union, as per the Chequers White Paper.

But after Salzburg that idea appears to have little hope of being embraced. So, the TCA will have to indicate the direction of travel, and that direction is likely to mean the UK staying de facto in a long term Customs Union with the EU.

But a more tricky part of this elaborate jigsaw relates to how all of this fits with the free trade negotiations, which are due to start within days of Britain leaving next March.

Any free trade negotiation is tit for tat. Access for one product requires reciprocal access for another.

If the EU grants London its UK-wide customs backstop, it is effectively granting the UK zero tariffs, zero quotas and zero rules of origin requirements in its access to the single market.

Obviously, the UK will have to concede its ability to do its own trade deals around the world, as it will have to submit to being part of the EU’s Common External Tariff (otherwise it doesn’t work for the Irish border).

But the EU would be offering zero tariff and zero quota access ahead of the main trade negotiations, taking perhaps their strongest cards off the table.

This gets us into the world of the "level-playing field", EU code for ensuring that, in the future, an economy the size of the UK’s does not undercut the EU by lowering environmental, social, employment, consumer protection and competition standards.

It is true that in the Chequers White Paper, London commits to maintaining high standards in these areas, in some cases offering to "non-regression clauses", or promises not to lower standards.

But again, this all relates to the future relationship, not the temporary customs union.

Under the EU’s "level playing field" mindset, member states will want to know that goods in the UK are not being produced more cheaply because the UK is not having to comply with the same environmental, consumer, health and social standards that they are.

While the EU will still carry out checks to ensure that goods coming from the UK comply with safety regulations, they cannot carry out checks to see if goods were made according to "level playing field" standards.

At the meeting of EU European and Foreign Affairs ministers in Luxembourg just before the 17 October summit, Michel Barnier raised these issues with member states. In turn, European capitals appear inclined to maintain a hard line on "level playing field" issues.

One of those issues is fisheries, and Mr Barnier made particular reference to it.

Britain leaving the Common Fisheries Policy (CFP) and "taking back control" of its waters is a totemic prize for Leavers.

However, the EU’s strongest card has been that the UK would keep its waters open for European vessels, otherwise it would be shut out from EU consumer markets (Britain essentially exports what it catches, and imports what it eats).

However, it’s understood Mr Barnier warned of the risk that if the EU agreed to a temporary customs union, it would be conceding its strongest card simply because of the UK-wide customs backstop.

Give the UK a tariff and quota free temporary deal, and the threat of limiting access for British vessels to EU markets vanishes, is the warning.

The other big long-term problem is the extent to which the future comprehensive free trade agreement between the EU and UK will be able to ensure no checks or controls on the Irish border.

London has always argued that that is really where the border issue will be resolved. But in order to keep the Irish border invisible, there would have to be high alignment in that future trade relationship, both on customs and on the regulation of industrial and agri food products.

The bad news is that the gruelling scrap over the backstop could simply be a precursor to a similar conflict down the line.

"In some ways the challenge in that future negotiation is going to be the new version of the current backstop challenge," says one source close to the negotiations.

"This idea that when we get to talk about the future relationship we’ll just be able to magically agree something that solves the border problem. We hope that will be the case. But implicit in that is some continuing close relationship.

"That’s obviously the current preferred direction of travel from London. But the people who want that will still tell you they want to be able to do third country trade deals as well. Right now nobody’s able to point to the magic formula that allows those two worlds to co-exist smoothly."

And right now, no-one can predict how all of these complex outworkings of the Brexit result will be processed by those men and women - Leavers and Remainers - who occupy the 650 seats of the House of Commons.

They will have to decide if Theresa May’s deal, if and when it comes, is worth it, if it "delivers Brexit", if it is a dog’s dinner, or if no deal is better.