has delivered a devastating defeat to Boris Johnson.

In a unanimous ruling, 11 judges have

ruled that his decision to suspend

Parliament, which was deliberating on Brexit,

was unlawful.

Here with me is Matthew Garrahan, the News Editor,

to discuss this, frankly, epic moment

in the history of Britain as a constitutional democracy.

MATT GARRAHAN: It was epic, Lionel.

How-- on a-- the scale of it, and the language,

the harshness of the language in this ruling

was quite unprecedented, wasn't it?

LIONEL BARBER: Well, Britain's Supreme Court

is only 10 years old.

It's not like the US Supreme Court that goes back to 1787.

But in a way, this was as big as a very important judgement back

in 1801, called Marbury versus Madison, where, essentially,

the US Supreme Court ruled against the executive,

and set out the parameters of power for the executive

and the legislature and the courts.

And this was this moment, even though we

have an unwritten constitution in the UK.

MATT GARRAHAN: Mm-hm.

And what do you think the immediate repercussions of it

will be?

LIONEL BARBER: Well, for Mr Johnson,

given the language, which was, again, ruthless,

it argued contrary to what the government said,

that this was a matter for the courts,

not just a matter of politics, that the executive had clearly

abused its powers, and that Parliament's role as holding

the executive to account, deliberating in public

on matters of state, that this-- all these matters

had been infringed.

So for Mr Johnson as prime minister,

he has some very hard questions to answer about

whether his position as prime minister is tenable.

MATT GARRAHAN: Which is quite something.

I mean, he's waking up in New York.

Currently, he's there on a visit--

LIONEL BARBER: To the UN.

MATT GARRAHAN: To the--

what does he do next?

I mean, Parliament will presumably reopen tomorrow.

And MPs will sit again.

What happens after that?

LIONEL BARBER: Well, first of all,

the court made clear that the Parliament had not actually

been prorogued because it was unlawful.

So they should, in fact, be sitting.

But they left it to the Speaker of the House of Commons, John

Bercow, to decide.

MATT GARRAHAN: Huge victory for him, isn't this?

LIONEL BARBER: A big one, and for Gina Miller,

by the way, who brought the suit in the first place

with Jo Cherry.

And by the way, another very important point,

that the Supreme Court ruled in exactly the same way as

strongly as the Supreme Court in Scotland, the Court of Session.

MATT GARRAHAN: Right.

LIONEL BARBER: So you have a sort

of unanimity between England, Wales, and Scotland.

That's important for the United Kingdom.

But what next?

Well, I think Mr Johnson's going to deliberate at the United

Nations with his inner circle.

And he's going to face a Parliament come back.

And he will have to answer questions

about whether his position is sustainable.

He's let it be known last night that he intended to stay on,

whatever the ruling.

MATT GARRAHAN: He also said he was going

to study the ruling carefully.

But we are in untested waters, aren't we?

I mean, for a British prime minister

to have been called in court that his actions were

unlawful is something we--

this is a new ground for us.

LIONEL BARBER: It definitely is.

And, you know, there is a history on Mr Johnson's

part of brazening things out, facing controversy,

from plagiarism to other matters, shall we say.

This, of course, is on a different scale.

This involves matters-- high matters-- of state,

constitutional propriety.

And just the way this thing was managed--

I mean, remember, he and his circle prorogue.

They decide to prorogue Parliament, ask

the Queen's support, which they got,

the royal assent for suspending Parliament.

I mean, essentially, the ruling supports the fact

that he misled the Queen.

MATT GARRAHAN: Yeah.

LIONEL BARBER: He said it was just to--

he wanted a new Parliament to discuss his new legislative

programme.

MATT GARRAHAN: Do you think, given this ruling, I mean,

the approach of his administration,

of his advisors--

Dominic Cummings, the key one--

has been to ride fairly roughshod over convention?

Do you think that this necessitates a change

if he stays?

LIONEL BARBER: I think it's important to recognise that Mr

Johnson and his Svengali adviser, Dominic Cummings,

said that in order to achieve Brexit,

we must get it by October the 31st, come what may.

MATT GARRAHAN: No ifs or buts.

LIONEL BARBER: No ifs or buts, because there's

been too much delay-- three years already

since the referendum.

And that's why they wanted to put pressure both on Parliament

and on the EU to get a deal.

There doesn't seem to be much progress here, by the way,

on that deal.

But my final point is that it's really important

to distinguish between constitutional propriety

and the Brexit question.

In effect, the judges were not saying

whether it was right to respect or not the referendum

result. They were saying the executive, Mr Johnson,

has infringed and abused his power regarding

Parliament's role.

And so that is quite different.

There will be people in the country--

and I'm sure some conservative newspapers--

who will denounce the judges as enemies of the people.

MATT GARRAHAN: Yes, enemies of the--

LIONEL BARBER: I think this is completely wrong.

It's very damaging for our democracy.

And they should respect the fact that this

was a unanimous judgement by the top judges

in the land on matters of constitutional propriety.

It goes to the heart of how our democracy can and should work.

MATT GARRAHAN: And finally, Lionel,

this case was so electric because it was in a sort

of grey area of our unwritten constitution.

There were some calls outside the court

that I heard just now for a more codified, formalised written

constitution.

Do you think that that is something

that we're going to get anywhere near in the--

LIONEL BARBER: I think it's premature--

MATT GARRAHAN: --coming months?

LIONEL BARBER: --to be moving towards a written constitution.

That's a very big move.

I think what you've seen today is the court adumbrate,

delineate the limits of power for the executive

and the role of democracy, of Parliament in our democracy.

That should be enough.

It should be enough to reflect on.

Let us just say this, though.

Given other matters of the constitution,

we know the strains within the United Kingdom.

We also know about the fact that maybe the House of Lords

isn't the most efficient--

it's a powerful scrutiny-- there are

other questions-- powerful scrutiny

of legislation, et cetera.

But there are some problems that we have.

But I think that's for another day.

What we should today celebrate is

that the judges stood up very clearly and unanimously

for the rule of law.

MATT GARRAHAN: Lionel, thank you very much.