Dark and dangerous threats against MPs like me are a sign No 10 and Cummings are getting utterly brazen

This has a strong whiff of the 1930s about it - it is a right wing, nationalist government's attempt to suppress dissent

Boris Johnson likes to hold himself up as a champion of democracy. Three months ago this week, in his first speech as prime minister outside No 10, he talked about Britain being the "home of democracy" and said our national flag - the Union Jack - stands "for freedom and free speech and habeas corpus and the rule of law and above all it stands for democracy". I don't disagree with him on any of those counts.

In this home of democracy, the government derives its mandate and legitimacy to govern by being able to command a majority in the House of Commons. Together with the House of Lords, the commons makes the laws and holds the government to account for its actions. The judiciary interprets and upholds the laws passed by parliament and the rule of law. This is how the separation of powers operates in the UK, with the legislature and our judges acting as a check and balance on the abuse of executive power.

And yet Johnson has shown a disregard for free speech and the rule of law and leads a right wing, nationalist Conservative government which, throughout the Brexit process, has attacked the institutions that safeguard our democracy. Sometimes Johnson has joined directly in these actions; on other occasions he lets fellow Brexiters within the nationalist, conservative ecosystem in and around his administration do his dirty work.

Viewed on its own, each attack by them on our democracy can be dismissed as the actions of a bunch of political fanatics; taken together, they are very dangerous and increasingly authoritarian.

In the 2016 referendum, just 37 per cent of registered electors (albeit 52 per cent of those who voted) supported leaving the European Union. But the issue of "how" we leave was reserved to parliament given it was undefined on the ballot paper. Vote Leave's victory in that campaign was treated by those who were part of it - ie Boris Johnson and many of his current ministers - as a licence to inflict whatever form of Brexit they deemed desirable on the country, no matter how damaging.

Importantly, they treated that vote - which is already over three years old - as an excuse to disregard the usual checks and balances which apply to stop the abuse of executive power in this country.

Every day Johnson and the Vote Leave cabal that run his party and his government invoke "the will of the people", not only to impose the most extreme form of Brexit but to justify breaking the law and undermining our democratic institutions. In short, they demand the complete subordination of every democratic institution to their extreme form of Brexit - for which there is no mandate - and are now turning to authoritarian methods in their quest to achieve this.

So, in his short time in office - he has been in the post for less than 100 days - Johnson has gone to unprecedented lengths to circumvent the system. Lying is usually the order of the day with the PM (anyone seen that £350m extra per week for the NHS yet?) but he has gone further than any other holder of the office since entering No 10, most notably by unlawfully suspending parliament in the weeks leading up to the possible departure of the UK from the EU without a deal, a crucial time in our history.

The Supreme Court performed its constitutional role by stopping him doing this last month and applying the law to the facts before it by reference to relevant statutes and case law. On reading their judgement you can see it is grounded in law and not politics. By convention, their independence is respected by all governments. Not this one.

The Leader of the House of Commons, Jacob Rees-Mogg, told ministerial colleagues privately that the judgement of the Supreme Court amounted to a "constitutional coup". Kwasi Kwarteng, the minister of state at the business department who also attends cabinet, went a step further and publicly went on the offensive against our judges.

He claimed that "many people up and down the country are beginning to question the partiality of the judges" and he said that "the extent to which lawyers and judges are interfering in politics is something that concerns many people".

This follows the accusations, before the Brexit negotiations even started, from Johnson's media cheerleaders (step forward The Daily Mail) that our judiciary are "enemies of the people" simply for doing their jobs. In that case the courts forced the government to get the consent of parliament before triggering Article 50. Not content with questioning their impartiality, those cheerleaders went after the judges personally and pored over their private lives.

Johnson was at it again this weekend, treating the law as something that applies to everyone else but him. The Benn Act required him to send a letter to the EU Council on Saturday evening requesting an extension to the Article 50 process in the event the House of Commons had not approved his withdrawal agreement with the EU, to safeguard against a no-deal Brexit on 31 October.

We voted against his agreement so he sent the letter unsigned, with a second letter in essence asking the EU Council to disregard the first letter sent under the Benn Act in an attempt to frustrate that law. Not frustrating the Act was something the government had given an undertaking to do in the Court of Session in Scotland. Whether he has frustrated that Act will be determined by that court in the coming days.

Then there is work parliament does holding the executive to account generally. At every step the right wing nationalists controlling the Tory party under May and now Johnson have sought to obstruct the people's representatives in parliament from doing their job of scrutiny of Ministers.

For example, they repeatedly refused at the outset to publish economic impact assessments of their Brexit proposals, only relenting when forced to do so by the House of Commons. In spite of the campaigning efforts of my Liberal Democrat colleague, Luciana Berger, in parliament to demand they do this in respect of Johnson's withdrawal agreement, they refuse to do so. It is worth remembering that the "meaningful votes", whereby the Commons approves the exit terms, were forced on the government at the start of the Brexit process - initially they had sought to exclude parliament from having much of a say at all.

It is true that MPs on both sides of the Brexit debate have been subject to abuse and threats for standing up for what they believe is in the best interests of their constituents and the country. This is totally unacceptable - but the intemperate language used by the PM and other ministers has only fuelled this.

However, the right-wing nationalists running the government are now taking things to an altogether different level - this is quite frightening, particularly if they were to get a majority at the general election whenever it comes. They are seeking to persecute and harass MPs by falsely accusing them of colluding with EU governments over Brexit. It is an absurd proposition given that the EU27 and the UK government are all working to ensure the withdrawal agreement Johnson has negotiated with the EU is delivered, and he himself wrote to them over the weekend urging them to ignore parliament's desire for article 50 to be extended.

In order to underline the point, his MPs are seeking to introduce a law to ban MPs - save for government ministers - from speaking to our partners and allies in governments around the world.

These accusations are made to call into question our loyalty and patriotism. Former Conservative backbenchers and ministers Oliver Letwin and Dominic Grieve, and Brexit Select Committee chair and former Labour minister Hilary Benn are reportedly under investigation.

This has a strong whiff of the 1930s about it - it is a brazen attempt to suppress dissent and persecute political opponents in parliament by this right wing, nationalist government.

One foreign office official put it well today when they said: "Threatening MPs with investigation is something you would expect the government to be stopping abroad, not encouraging at home." It represents an attempt to fundamentally breach our constitutional and our human rights - threatening our democracy.

Given the gravity of this issue, I have written to the prime minister demanding he clarify whether any such investigation is under way or whether this is over-briefing from Dominic Cummings and friends. I have also demanded he rule out introducing any law seeking to prevent parliamentarians from speaking to other governments - we cannot properly scrutinise government foreign policy if we are prevented from doing so.

If he fails to give these assurances, we can take it as a given that another term of a Tory government will be altogether more authoritarian than any government we have seen in a generation. Another reason to vote them out when the time comes.

Chuka Umunna is the Liberal Democrat MP for Streatham