In November 2003, two days after he was forced to step down as party leader, Iain Duncan Smith was honouring a charity engagement at the Adjournment restaurant in Portcullis House. Entering the swarming room, he was horrified to discover that nobody came to say hello or even looked his way. As he was making small talk with his press officer, a woman darted past guests and hugged a relieved Duncan Smith. It was Cherie Blair.
A member of his then shadow cabinet recalls: "What was he to do? He was no William Hague. A life of writing award-winning books on Pitt the Younger, newspaper columns or making them roll in the aisles at corporate dinner parties was not going to happen for Iain." Duncan Smith could be difficult; "grumpy" and "rude" are the printable descriptions of a man who was capable of upsetting his most loyal colleagues.
Four years on, the self-styled "Quiet Man" has been on the slowest of burners, starting up the Centre for Social Justice with the aim of finding effective solutions for poverty-stricken areas of Britain. Shunning publicity, IDS has held the occasional press conference attended by charity workers and a handful of journalists hoping for a sensationalist story. They find a man, passionate about his projects and determined to narrow the gap between rich and poor. As an old friend explains, "It's hard to describe. Iain has changed. He's lost the chippiness; there's a rawness about him as if the humiliation of 2003 has made him."
It was for those reasons that David Cameron asked Duncan Smith for policy recommendations on society. The result, after 18 months of consultation with more than 800 experts, orga nisations and charities, is Breakthrough Britain, which puts forward a different approach to tackling poverty in the UK. This has produced vast amounts of coverage and debate, specifically on controversial plans for marriage tax breaks.
A member of the Duncan Smith 2003 team is surprised how he has emerged: "It struck me that Iain was going to get bitter. He was always irritable, made me drop off his dry-cleaning, and lacked patience. It's very interesting to see a man come into his own, and he's proved his worth."
A colleague at the Centre for Social Justice appears to have a far better understanding of Duncan Smith than anyone who worked under him as party leader: "Iain's background - a military family, Roman Catholic - pigeonholes him as a far-right, hard-hitting tax-cutter, but he is much more complicated than that. When he was leader, he visited Easterhouse in Glasgow and was appalled by poverty on a scale he had never witnessed before. Something twigged - he was sitting in a living room drinking tea and eating Garibaldi biscuits and hearing tales of utter despair. It changed his life."
Current staff at Conservative Party head quarters, many of whom never experienced the political Fawlty Towers that was Central Office of 2003, find it hard to believe just how bonkers IDS's past few weeks have been.
What makes Cam eron the liberal moderniser, the bright young thing, turn to Duncan Smith for direction? One might say it is to appeal to the grass roots, the Tory faithful who liked his staunch right-wing credentials, but it's not; it's more than that.
A Tory MP who was one of the first to express no confidence in IDS as leader concedes: "Iain is very much the agenda now. He has reinvented himself, he's grafted, and he's done it with a will and a 600-page document."
After hearing him on the Today programme, one less enthusiastic shadow cabinet MP says: "The whole marriage idea is slightly soft around the edges; we've got to bite the bullet. It's a gesture that says to the Daily Mail, 'Please don't carry on your love-in with Gordon.'"
Another is worried by the moral elements of the proposals. "It's high-risk, after the disaster that befell John Major with 'Back to Basics'. I'm worried about getting our fingers burnt."
The right has been crying out for Cameron to talk about the family. An aide to the party leader points out: "Nine months ago, IDS was worried Cam eron may not be in tune with his thinking, but over the past six months, David has become increasingly supportive."
The Tories will launch "Stand Up, Speak Up - the Nation's Despatch Box" (embarrassingly new Labour as this sounds). A press officer assures me that it is no gimmick: "Schooling with a parent-power-driven approach and welfare reform will both come out as battleground areas. Conservatives will accuse the government of maintaining people in a state of poverty. With immigration and crime, both parties have roughly the same agenda. At last, now we differ."
A man who was thought to have achieved so little as party leader has found his calling. He says: "I do not claim to have all the answers, but I believe my case for change has something to offer a country sick of government by spin."
Even the still-present cough seems to have become slightly less tickly.