If there is one thing in short supply in parliament these days, it is people who fret about detail. Margaret Thatcher read every paper in her red box. Robin Cook, too, got the importance of detail, and was almost certainly the only one who was really on top of what his government was doing in Iraq. The same might be said about Tam Dalyell, who was all over the Falklands conflict.

I’m not sure when exactly it started to become the fashion in Westminster to skim-read documents, only bother with bullet points or, worse, to take them entirely on trust – but that, perhaps, was when we began as a country to lose our way.

The whole Brexit saga is, in my view, one big, terrifying leap in the dark. We can’t even say, as a nation, that we are taking calculated risks, as we haven’t had the information on which to base the calculations. This disturbs me. My day job, running a fund management company, means I know that I and my team can’t afford not to read every word of every document about assets or markets we propose to invest in, and to be absolutely clear we are complying with all the legal and regulatory requirements involved.

If only politicians had such formal obligations to voters. Ever more momentous decisions are being made in government on the basis of little more than a whim or political expediency. The questions that began to occur to me after Theresa May announced her “confidence and supply” agreement with the Democratic Unionist party (DUP) – in other words, the £1 billion “bung” for Northern Ireland designed to sustain her government in power – seemed to me to be obvious and pressing. Only no one seemed minded to ask them.

After my successful high court and supreme court actions to guarantee parliament’s right to have its say on triggering article 50 , I had no particular appetite to put my head above the parapet again. What has struck me about the political world, as opposed to the business world, is that rational discourse has become all but impossible. All too often, arguments are conducted not on the basis of facts but on the basis of emotion – and, honestly, it is no fun being abused in the pages of tabloid newspapers or online.

I was, however, emboldened by Jason Moyer-Lee, general secretary of the Independent Workers Union of Great Britain , a good, decent campaigning trade union that has worked hard to make sure that the likes of John Lewis and the Royal Opera House adhere to the London living wage. Moyer-Lee and I both felt that if no one else was going to do anything, then it was down to us to act, irrespective of whether it would lead to intimidation and harassment. So we engaged lawyers – all working pro-bono – to test whether our laws were being adhered to in respect of the Northern Ireland payment. On 7 August we fired off what is called a pre-action protocol (PAP) letter to the government.

To our great surprise, the government’s lawyers responded by making an extraordinary admission. “No additional funding contemplated by the agreement [with the DUP]has yet been made available and no timetable has been established for the provision of funding,” their letter said. “We have also explained that additional payments contemplated by the agreement will be authorised by parliament.”

We were stunned. At no time, either when May struck the deal with the DUP or since, had the government admitted it required prior parliamentary authorisation before taxpayers’ money could be handed over to Northern Ireland. By never disclosing this crucial detail, senior members of the government look very much as if they had intentionally misled parliament, the parliamentary Conservative party, the public and, quite possibly, their prospective partners, the DUP.

It is telling that barely 48 hours after I revealed the need for parliamentary approval for the £1bn payment, the DUP was suddenly siding with the opposition against the government in a non-binding vote on the totemic issue of tuition fees, a policy originally dreamed up by Labour.

I question when, if indeed ever, the government intended to tell the truth, especially when both parties have repeatedly said that the first payment to Northern Ireland would be made this autumn. Both parties may well have claimed there is nothing “new or surprising” in what I have revealed about the £1 billion payment, but their legal team told a different story. “Proposals for central government funding are put before the House of Commons in the form of main and supplementary estimate,” they said in their letter. “Estimates are subject to a vote in the House of Commons and are typically subject to debate in that house.”

Something just doesn’t add up. On the one hand, senior DUP members were vocal about pressing for a payment as soon as this October, but the central government supply estimates 2017-18 covers supply estimates for the year to 31 March 2018, which would mean the new legislation permitting this payment, even if as the government suggest “is a mere formality”, would not allow for it until the next financial year, commencing April 2018. Similarly, the budget doesn’t take place until 22 November, so it looks like the government’s IOU is getting bigger by the day. This doesn’t speak very well to the government’s commitment to open dealings with its parliamentary partners, nor its sense of accountability to parliament and the public. With the government saying that no timetable has been set for parliamentary authorisation of this additional payment to Northern Ireland, the question remains: when?

We need to be absolutely clear about what all this means. Last week, the government asked MPs to approve its keystone European Union (withdrawal) bill, granting it sweeping new “Henry VIII” powers that will allow ministers to meddle with our basic freedoms as they see fit, away from parliament and the scrutiny necessary to ensure our rights and protections are not diminished or extinguished. MPs need to fear the worst when it comes to what this government may do without proper parliamentary scrutiny. The British public deserves better than a government blatantly attempting to put itself above the law and seeking to bypass parliamentary scrutiny simply to cling to power. It is aware that the public – and perhaps some sections of the press – have become apathetic, and takes it for granted that awkward questions will not be asked. If there is one lesson to be learned from all this, it is that we need to watch this government – and all future governments, for that matter – like a hawk, and be prepared to ask awkward but legitimate questions. The price of liberty, as Thomas Jefferson so rightly said, is eternal vigilance.

Gina Miller was the lead claimant in the successful legal fight for a parliamentary vote on article 50

Guardian Service