[nomadking]

Originally Posted by Hugh

Once again, your expert legal advice is much appreciated - you and nomadking should get together and provide BJ/Cummings with legal support, to avoid further fiascos like Prorogation being declared null and void.

It is completely undeniable that the WA, as the EU specifies that it is be transitional(check your dictionaries) and unambiguously limited in time.
Link

In his presentations to the European Parliament, Barnier has stressed a number of principles for the negotiations: the four freedoms must be indivisible; any transitional agreement must unambiguously be limited in time;

It also refers to a 2nd future(check your dictionaries again) agreement. Any contract or agreement anywhere else in the World that contained something of the nature of the backstop, ie not transitional, and unambiguously not limited in time, would be ruled invalid and illegal. It is also undeniable that the Irish intention of the backstop is impose it in one way or another outside of any future 2nd agreement. It is all incompatible with the EU treaty.
Link about Article 50.

2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. That agreement shall be negotiated in accordance with Article 218(3) of the Treaty on the Functioning of the European Union. It shall be concluded on behalf of the Union by the Council, acting by a qualified majority, after obtaining the consent of the European Parliament.

The onus is on the EU to reach an agreement that is transitional and unambiguously limited in time.

The backstop could validly be part of the framework of the future relationship(ie the political declaration), but that political declaration is not legally binding on the UK and probably not on the EU. Although I'm not quite sure what, if anything, is ever legally binding on the EU.
Link

The draft political declaration on the future relationship between the EU and the UK, after Brexit, is out. Theresa May describes it as the right deal for the UK.
A few points to remember…
This is not a legally binding document.
It's not very long either, but it has grown from last week's seven-page outline to 26 pages. It sits alongside the 585-page Draft Withdrawal Agreement (which will be legally binding if it gets ratified).

What is deniable about any of that? A contract that is legally declared to have to be temporary and limited in time, cannot be legally valid to have a condition, that is not temporary or limited in time? Be interesting to know about the vast number of legal agreements, that certain people seem to think exist, that have a permanent condition applied in a temporary arrangement.
Link

Assuming then that transition can be achieved on the basis of Article 50 TEU, does the transition have to be time-limited? It would seem clear from the wording of Article 50 that it is confined to agreeing the terms of withdrawal and cannot serve as a basis for a (permanent) future relationship. This would suggest that a time limit must be included and indeed, the Commission’s draft provides that the transition period ends on 31 December 2020.

Regardless of whether the backstop is in the WA(ie Transitional agreement), the conditions set out(eg the backstop) cease to apply.

Looks like any WA has to presented to Parliament more than 3 weeks before any debate and vote.
Constitutional Reform and Governance Act 2010(under Gordon Brown)

20Treaties to be laid before Parliament before ratification
(1)Subject to what follows, a treaty is not to be ratified unless—
(a)a Minister of the Crown has laid before Parliament a copy of the treaty,
(b)the treaty has been published in a way that a Minister of the Crown thinks appropriate, and
(c)period A has expired without either House having resolved, within period A, that the treaty should not be ratified.
(2)Period A is the period of 21 sitting days beginning with the first sitting day after the date on which the requirement in subsection (1)(a) is met.
(3)Subsections (4) to (6) apply if the House of Commons resolved as mentioned in subsection (1)(c) (whether or not the House of Lords also did so).
(4)The treaty may be ratified if—
(a)a Minister of the Crown has laid before Parliament a statement indicating that the Minister is of the opinion that the treaty should nevertheless be ratified and explaining why, and
(b)period B has expired without the House of Commons having resolved, within period B, that the treaty should not be ratified.
(5)Period B is the period of 21 sitting days beginning with the first sitting day after the date on which the requirement in subsection (4)(a) is met.

25Meaning of “treaty” and “ratification”
(1)In this Part “treaty” means a written agreement—
(a)between States or between States and international organisations, and
(b)binding under international law.

From transcript of Santos & Miller case

SANTOS & MILLER
Applicants
-v-
SECRETARY OF STATE FOR EXITING THE EUROPEAN UNION
Respondent
...

18 MR EADIE: But if there was an Article 50(2) withdrawal
19 agreement, that would be a treaty between the
20 United Kingdom and the EU.
21 THE LORD CHIEF JUSTICE: Yes.
22 MR EADIE: As such, it is likely that it will come within
23 the procedures in CRAG. You have CRAG behind tab 29 in
24 bundle C.
25 THE LORD CHIEF JUSTICE: Yes.

Official government Explainer on the WA

16. The Withdrawal Agreement will also be subject to the provisions of the
Constitutional Reform and Governance Act (CRaG) 2010. Following this, the treaty
will be ratified, and can enter into force.