Here’s the Daily Mail’s comment the morning after: “In an act of betrayal and dishonesty, the House of Cronies, Dodgy Donors and Has-Beens voted last night by 358 to 256 to amend the Brexit Bill.”

Warnings that the upper house will be “signing its own death warrant” may come oddly from the Mail, not a vociferous supporter of reform until now. But hey, Brexit makes all kinds of strange new bedfellows

The Lords debate exposed the prime minister’s contradictory and deceitful arguments against protecting EU citizens living here. If, on this most popular and painfully human question, she will give no inch, that’s a terrible augury for how she intends to conduct these negotiations, opening with a war cry to all 27 countries: we hold your people hostage.

The Mail says: “It’s the bloody-minded Brussels bureaucracy, not her, that is bargaining with family lives and happiness.” Because, of course, she is “pushing hard for a deal that upholds the rights of all expats”. This is just a “remoaner” wrecking tactic, “a naked bid to sabotage Brexit by creating difficulties for Mrs May”.

Lords urge Tories to back Brexit bill amendment on EU citizens Read more

As the Guardian reports heart-rending cases of threats to longtime EU residents with British spouses and children born here, Helena Kennedy gave the shocking statistic that a third of all their applications for residency are being turned down by the Home Office. Whoever knew that if they hadn’t had private heath insurance in the past they could be cast out for all time?

Yet one Brexit peer after another rose to swear there was never any question of expelling them. Ministers, including the foreign secretary, have assured the TV cameras it will never happen. But if so, why not accept this amendment with good grace when it returns to the Commons?

No, they say: these 3 million people must be used as hostages – though representatives of the 1.2 million Britons in the EU say they want this amendment passed, as an act of goodwill. You can’t bargain unless you sincerely mean to carry out the threat. So which is it?

Mass expulsions would be unthinkable – May as the new Idi Amin? Besides, for a depleted police, border force and administrators, it would be a crippling near-impossibility. Are we really to say goodbye to 55,000 doctors and nurses, a million care workers and prized university students while devastating industries from agriculture to car-washing, hi-tech IT to finance, catering and tourism? Forget tourism entirely – we would become pariahs.

So which is it: they can definitely stay – in which case just accept that amendment and tell the world – or rattle a sabre you may then be forced to use, whatever the self-harm?

Nigel Lawson won top marks for the most duplicitously twisted argument: he was voting against because this amendment would “stir up fear” in these EU residents, when there is “no question” of their expulsion. All this, he said, was just “virtue-signalling”, the new all-purpose insult for anyone the right opposes.

Presumably there are “sin-signallers” – including the 24 bishops who disappointingly didn’t vote for the amendment, led by John Sentamu, the archbishop of York. Only two bishops rebelled.

The poisonous rancour of Norman Tebbit is nothing new, but even their lordships gasped at his complaint about “looking after foreigners and not the British”.

Next deceit: the government claims this would delay triggering article 50, yet all it has to do is accept it with no delay at all. Besides, May’s timetable is plucked out of the air, insensitively ill-timed for distracted French and German leaders facing elections.

Martin Rowson on Theresa May's defeat in the Lords – cartoon Read more

Bob Kerslake, former head of the civil service, made another killer point, dismissing promises a quick deal on this could be first priority in May’s negotiations: “The government does not have the power to strike a deal with the EU quickly because it is not in the UK’s gift.” Experienced diplomats rose to agree: there may be no agreement on anything until there is an agreement on everything. That might take years.

Every one of the 27 countries, plus their parliaments and the European parliament has to agree every aspect of a deal. If this is the tone in which the UK proceeds, then throwing spanners in May’s works will be irresistible to many of them. Why not instead welcome with open arms all our much-wanted and needed EU friends and neighbours who are already settled here?

This is just round one, but the bitterness and loathing of the victorious Brexiteers is a mystery. They won. Brexit is happening. But everywhere they spy conspiracies and betrayals, still spoiling for a fight. Why no magnanimity?

Ahead lie thickets of fiendish issues, subtle and dangerous. Is this how they will approach all debate, so any suggestions are howled down as a 48% plot? If so, things can only get worse.