Supreme Court: The key lines of the judgement

President of The Supreme Court, Justice Lady Brenda HaleEPA
By Dominic Casciani
Home affairs correspondent

The President of The Supreme Court, Justice Lady Hale, has read out the court's judgement that the decision to prorogue - or suspend - Parliament was unlawful.

Here are some of the key sections of the ruling:

Text from judgment saying: A decision to prorogue Parliament... will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions... In such a situation, the court will intervene if the effect is sufficiently serious to justify such an exceptional course.

Why does this matter?

The Supreme Court has drawn a clear line in the sand that a prime minister's executive powers in this most important area of how and when Parliament opens and closes are now curtailed - for ever.

Text from judgment: The Government exists because it has the confidence of the House of Commons. It has no democratic legitimacy other than that... The first question, therefore, is whether the Prime Minister's action had the effect of frustrating or preventing the constitutional role of Parliament in holding the Government to account.

Why does this matter?

The Supreme Court has underlined that the government and prime minister are the "junior" partners in the British constitution - that Parliament is the "senior" partner - and the junior cannot tell the senior, which acts for the people, what to do.

Text from judgment: This was not a normal prorogation in the run-up to a Queen's Speech. It prevented Parliament from carrying out its constitutional role for five out of a possible eight weeks between the end of the summer recess and exit day on the 31st October.

Why does this matter?

The Supreme Court is underlining that if there is an exceptional use of executive powers by the prime minister that infringes on parliamentary democracy, judges have the power to intervene.

Text from judgment saying: It is impossible for us to conclude, on the evidence which has been put before us, that there was any reason - let alone a good reason - to advise Her Majesty to prorogue Parliament for five weeks, from 9th or 12th September until 14th October. We cannot speculate, in the absence of further evidence, upon what such reasons might have been. It follows that the decision was unlawful.

Why does this matter?

This is the most important paragraph.

During the case, the prime minister failed to provide any evidence to the court about his intentions - there was no witness statement.

This contributed to the Scottish Court of Session's inference that he had an improper purpose - and the Supreme Court's scathing conclusion that the highest court in the UK has seen no evidence to explain what he was doing.

Text from judgment: As Parliament is not prorogued, it is for Parliament to decide what to do next. Unless there is some Parliamentary rule to the contrary of which we are unaware, the Speaker of the House of Commons and the Lord Speaker can take immediate steps to enable each House to meet as soon as possible to decide upon a way forward.

Why does this matter?

In its last submissions last week, government lawyers argued that the prime minister retained the power to decide how and when to recall Parliament - and even to "re-prorogue" it.

The 11 justices have unanimously rejected that plea.

Text from judgment: the courts have the responsibility of upholding the values and principles of our constitution and making them effective. It is their particular responsibility to determine the legal limits of the powers conferred on each branch of government, and to decide whether any exercise of power has transgressed those limits. The courts cannot shirk that responsibility merely on the ground that the question raised is political in tone or context.

Why does this matter?

The Supreme Court was set up to resolve the most complicated legal and constitutional questions of the day - and in this judgement it has shown it is not afraid to tread into matters that judges in previous eras would have feared to have been too political.

And this is why this judgement is so important for the future of the British constitution.