What parts of EU law impose that the EU cannot consider an extension/delay request not coming from the PM?

Question

A recent article quotes Boris Johnson as saying

"The EU is obliged by EU law only to negotiate with member state governments, they cannot negotiate with Parliament, and this government will not negotiate delay." [Johnson said].

An slightly older article of the BBC commented however that

Parliament may have passed a law instructing the government to request a new extension if a Brexit deal isn't reached by mid-October. But if Boris Johnson refuses - as he insists would be the case - then EU leaders would normally listen to him, their peer, as head of Her Majesty's government.

EU sources point at Spain (and the Catalan issue) as to why leaders alone - not parliaments - represent member countries at the EU table.

But as so often when it comes to Brexit, this situation is messy.

In fact, EU lawyers won't give a definite answer as to what the EU would definitely do if, with a no deal Brexit looming, parliament demands a new Brexit extension while the prime minister says no.

EU rules on how to deal with a departing country - the so-called Article 50 text - don't specify that an extension request must come from a government but rather from "the member state concerned".

The EU could offer an extension unprompted but the decision to trigger one has to be unanimous amongst EU leaders and the UK.

This is a real nail-biter for EU leaders. They have so wanted to stay out of UK domestic politics, but if and when it comes to the extension debate, they could find themselves slap bang in the middle of the fight between parliament and the PM.

So, is there some other EU law that forces the EU to listen to no one but the UK PM on this extension issue? (Because article 50 seems rather ambiguous.) Or is this simply a matter of diverging interpretations of the same text?

Answer 1

Article 50 requires the member state to act in accordance with its constitutional requirements.

The precedent so far, including the Article 50 notification and subsequent extension, suggests that both sides recognize that in the case of the UK this means the government making the request. A change of this EU interpretation of UK constitutional law would require an explanation.

Answer 2

The most relevant provision is probably the Treaty on the European Union, Article 10:

Article 10

1. The functioning of the Union shall be founded on representative democracy.

2. Citizens are directly represented at Union level in the European Parliament.

   Member States are represented in the European Council by their Heads of State or Government and in the Council by their governments, themselves democratically accountable either to their national Parliaments, or to their citizens.

See also Protocol 1 of the treaty, which makes it fairly plain that the EU deals principally with governments, not parliaments.