David Cameron sat impassively, staring into his Zoom camera, as one of his most famous barbs was thrown back at him by Labour MP Rushanara Ali: “You were the future once.”

Cameron may have wished he had never aimed that comment at Tony Blair in 2005, as his efforts to explain away the Greensill Capital lobbying affair reinforced the old adage: there is nothing as ex as an ex-prime minister.

The former Conservative prime minister endured the darkest of days on June 24 2016 after presiding over the UK’s referendum vote to leave the EU, but on Thursday he suffered a ritual humiliation at the hands of MPs.

Cameron’s insistence that his epic lobbying efforts for Greensill Capital were motivated by a desire to help small companies during the Covid-19 crisis — not his own bank balance — set the scene for a toe-curling Thursday afternoon.

Mel Stride, Tory chair of the House of Commons Treasury select committee, tried in vain repeatedly to coax out of Cameron the “delicate” issue of how much money he was originally due to secure for his efforts on behalf of the now failed supply chain finance company.

Angela Eagle, a Labour MP, said his barrage of 56 texts to ministers and officials in an attempt to win Greensill access to government-backed Covid loans was “like stalking”. Siobhain McDonagh, another Labour MP, said Cameron had demeaned himself by “WhatsApping his way around Whitehall”.

Cameron, who commanded British politics until his decision to hold the Brexit referendum, was reduced to answering questions about why he signed a text to Tom Scholar, the most senior mandarin at the Treasury, “Love, DC”.

The former premier claimed he always did this, even though his children said it was “old fashioned and odd” to sign text messages. It was pointed out that he did not say “Love, DC” in his text to Cabinet Office minister Michael Gove, who was on the opposite side to Cameron in the Brexit referendum.

Cameron’s words from his political pomp kept returning to haunt him as he endured the Westminster equivalent of a lengthy spell in the pillory: two back-to-back grillings from Commons select committees.

He was reminded of how he had said in 2010 that lobbying would be “the next big scandal”. Now he finds himself in the middle of one, apparently by accident.

“I was not employed by Greensill as a lobbyist,” he said. “That was not intended to be part of my role.” Instead, as the coronavirus pandemic hit, he went into action for his employer to try to secure government help.

Cameron said his role at Greensill was to try to win new business and offer geopolitical advice, claiming this did not provide him with any great insight into the company’s impending collapse.

He was at pains to insist he was an employee, not a director. And certainly, he stressed, he was not a “shadow director”, pulling the company’s strings from afar; most big decisions were being taken outside of his sight.

More broadly Cameron, his familiar smooth features occasionally looming large on the video camera, suggested he was simply doing his best to make his way in the political afterlife, without any clear guide on how to do it.

“There really isn’t a road map for an ex-prime minister, particularly for a younger one who doesn’t just want to be on the board of some big bank and make the odd speech around the world, but who wants to get stuck in to help business expand,” he said.

That did not elicit much sympathy from the MPs, but Cameron did make some concessions. He admitted former prime ministers were in a “different category” and that while he had not breached any lobbying rules, conduct was important.

He repeated his main admission that he should have sent formal letters or emails, rather than texts, to the ministers and civil servants that he lobbied. The body that policed private sector jobs for former ministers and senior officials needed more teeth, he suggested.

Cameron said it was “very depressing” to have worked for a company that collapsed, insisting he had carried out “due diligence” on Greensill before signing up.

One friend of the former prime minister insisted the MPs had “not landed a blow” on Cameron during several hours of testimony. Another said he was the “wrong villain” in the Greensill saga, and that his main offence was “sending unsuccessful text messages”.

But it was nonetheless a chastening afternoon for a former prime minister whose post-Downing Street business career has scarcely blossomed: Greensill, a yet-to-be-launched UK-China investment fund and a public-speaking career truncated by Covid-19 feature on his CV.

“You’re famously known as Teflon man, you’re a great survivor,” said Ali, but it was not a compliment. “Your reputation is now in tatters, Mr Cameron.”