In a substantial twist in the Brexit situation we now have the High Court's decision. It would be unlawful for the Government, without reference to Parliament, to notify the European Union of Brexit, and so start the formal two year process of the UK's withdrawal from the EU.

The legal question in the case was whether, as a matter of constitutional law, the Crown (ie the Government) is entitled to use its prerogative powers, without reference to Parliament, to give notice under Article 50 for the UK to cease to be a member of the EU.

It was agreed by all sides, that this question is one that the courts are able to consider and decide. This case was not about examining the referendum or its outcome.

The court did not accept the argument put forward by the Government and expressly accepted the claimants' principal argument. Because the inevitable effect would be to take away UK citizen's rights granted by Parliament, the claimants' had argued that the Government alone cannot lawfully trigger Article 50 without reference to Parliament.

The claimants' argument was built on the fundamental principles of the UK constitution. The Crown's prerogative powers cannot be used by the executive government to diminish or abrogate rights under the domestic law of the UK (whether conferred by common law or statute), unless Parliament has given authority to the Crown (expressly in or any necessary implication from the terms of an Act of Parliament) to diminish or abrogate such rights.

The High Court concluded that the European Communities Act 1972 was enacted as a statute of major constitutional importance – it can only be repealed in any respect if Parliament makes it especially clear in the later repealing legislation that this is what it wishes to do. The court stated "Parliament having taken the major step of switching on the direct effect of EU law in the national legal systems by passing the [1972 Act] as primary legislation, it is not plausible to suppose that it intended the Crown should be able by its own unilateral action under its prerogative powers to switch it off again"[paragraph 87] and "(…) still less can it be thought to be likely that Parliament nonetheless intended that its legal effects could be removed by the Crown through the use of its prerogative powers". [paragraph 88].

The Court held that Parliament intended with the 1972 Act to legislate to introduce EU law into domestic law. This included creating rights for British Citizens and companies in relation to their activities in other Member States, for example pursuant to rights of free movement of persons and of capital and rights of freedom of establishment (referred to as category (ii) rights).

A removal of such citizen rights, the court ruled, is beyond the power of the Government alone.

The effect of the decision today will, as has been stated by the Government, be an appeal. So there will be further legal consideration of the question. There will also be a political effect as the decision must throw significant doubt on the Government's well-publicised schedule of triggering Article 50 by March 2017.

The appeal will go straight to the Supreme Court with a hearing being provisionally set over two days in the second week of December 2016 (to be heard by all 11 Supreme Court judges). A judgment may then be expected around the New Year.

If the High Court's decision is upheld by the Supreme Court, the next step is for the Government to arrange a vote in Parliament to approve triggering Article 50. While the timeframes for a Parliamentary vote are uncertain, the results of such a vote could be far-reaching.

The political question which many have been asking is whether the MPs in a vote would automatically confirm the EU Referendum outcome? We have only just seen the start of the political positioning on the next steps, which will generate much further commentary. What the decision has done is to reinforce the separation of powers within our democracy.

The uncertainty for UK PLC remains pending the outcome of this case. The relative fast pace with which the Supreme Court is likely to hear the case is welcome. Businesses cannot properly plan whilst there is doubt on the final outcome.

For more information, please look at the full judgment: R (Miller) -V- Secretary of State for Exiting the European Union.