Listening to debate in @HouseofCommons : there seems to be a dangerous illusion that the UK can benefit from a transition in the absence of the WA.
Let me be clear: the only legal basis for a transition is the WA. No withdrawal agreement means no transition.

— Michel Barnier (@MichelBarnier) March 12, 2019

Asked what constituted a "reasoned request" he said, "I will not venture into a typology on what a reasoned request would be. I would simply state the obvious that a reasoned request is a request based on a reason."

"We were and remain happy to apply the backstop to Northern Ireland only if they want to go back to that," he said.

... This impasse cannot be allowed to continue. In the UK it is creating and doing damage to faith in politics, while the European Union has a legitimate desire to move on to decisions about its own future. That is why the Government has decided to take further action to seek a consensus across the House of Commons on the right way forward.

The Government's policy has always been and remains to leave the European Union in an orderly way, and without undue delay. The House of Commons has not thus far approved the deal ...

T. May, A letter from Prime Minister Theresa May to European Council President Donald Tusk, 5 April. THREE (3) PAGES

Diversity is the key to economic and political evolution.

RECALLING that the Joint Report from the negotiators of the European Union and the United Kingdom Government on progress during phase 1 of negotiations under Article 50 TEU on the United Kingdom's orderly withdrawal from the European Union of 8 December 2017 outlines three different scenarios for protecting North-South cooperation and avoiding a hard border, but that this Protocol is based on the third scenario of maintaining full alignment with those rules of the Union's 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, to apply unless and until an alternative arrangement implementing another scenario is agreed,

• Clause 21 (inserts new section 8C  into the EU (Withdrawal) Act 2018)
  
• New section 8C(1) confers a power on a Minister of the Crown in connection with the Ireland/Northern Ireland Protocol in the Withdrawal Agreement New section 8C(6) places a duty on a Minister of the Crown to define the term 'qualifying Northern Ireland goods'
  
• A  power to implement the Protocol on  Ireland/Northern Ireland. A duty to define the term 'qualifying Northern Ireland goods'
  
• Draft affirmative procedure where a statutory instrument [SI] under new section 8C(1) amends, repeals or revokes primary legislation or retained direct principal EU legislation; [...]

It replaces the ["]backstop["] provisions  in the old Withdrawal Agreement negotiated by the former Prime Minister and rejected by Parliament with a system whereby Northern Ireland remains aligned with EU regulations on goods (including certain laws for VAT on goods).

No tariffs will need to be paid on goods moving from GB to NI, which are not at risk of moving to the EU. Thus the Protocol applies EU tariffs in Northern Ireland except for movements within the single customs territory of the United Kingdom.