The Mirror's "editorialisation" of the issue - personal attacks of this kind on editors are so rare as to be almost unheard of - led Dacre, who apparently failed to see the funny side, to complain that Mirror editor Piers Morgan's publication of the sumo picture demeaned the profession of journalism. That depends, of course, on what you think of the profession. Nonetheless, it was an odd end to a bizarre week which kicked off last Monday with a bitchy Mail attack on Posh's fashion sense after she wore a Flintstone-style red mini skirt to a party in London.
By Tuesday, however, the offending skirt did not just expose Posh's lack of taste. According to the Mail it also laid bare what it had already suggested in the weeks previous, that Posh, "bones showing", was worryingly thin, perhaps even anorexic.
By Wednesday The Mirror had waded in to champion Posh's cause. Posh's claim that she was not anorexic, but in fact fit and well, ran on the front page along with her allegation that the Mail had deliberately used pictures that made her look skinnier than she was. But the Mail pressed on. On Thursday the opinions of experts, writers and parents were published and they invariably concluded that Victoria was too scrawny and a dangerous example to the young. On Friday the Mail attacked not just Posh but her footballer hubby, David Beckham, suggesting his jet-setting lifestyle was interfering with his performance for Manchester United.
Beckham, like Posh, is a regular target for the Daily Mail, which seems to consider the pair vulgarly nouveau riche and their icon status proof, as if any were needed, that Britain, under New Labour - another Dacre detestation - is going to the dogs.
None the less, on Friday The Mirror seemed to cross a line by pulling Dacre so explicitly into the fray and inviting readers to vote on who had the best body, Dacre (as sumo) or Posh.
Yesterday, the row was still rumbling on. In a review of the Spice Girls' first concert for almost a year, the Mail again referred to the replacement of the once-voluptuous Posh by a sinewy elfin. Incongruously, the review appeared on the very same day as the Mail published its cabbage soup diet in which a loss of 10lbs in just seven days was promised to women struggling to get into some kind of shape for the Christmas party.
Meanwhile, The Mirror, under the headline "Stunning Spice", seemed to have concluded that Posh, who danced for more than an hour on stage, was just too energetic to be suffering from an eating disorder of any kind.
A view that offered its own internal inconsistency for Dr Miriam Stoppard, The Mirror's medical guest writer, warned in the early days of the Mail- Mirror war that anorexic girls are often vibrant and enthusiastic "flushed by the success of what they do best - staying thin".
So just what was last week all about? The official response at the Mail is "no comment". But off the record a senior source plays down the dispute, dismissing it as an everyday event in the competitive wacko world of high- circulation tabloid newspapers. The source also insists that Mr Dacre does have a sense of humour and that, despite claims that he was furious last Friday, that he "probably" laughed at the sumo picture. The insider adds the qualification that he was, of course, not there when Dacre found out. He insists that there was, and still is, no personal animosity between Dacre and Piers Morgan.
"The problem with the Mail is that people are jealous of its on-going success," says the senior source, giving the impression that the Mail is not at all bothered by the antics of the rival snapping at its heels. With the latest circulation figures showing the papers neck and neck - The Mirror at 2,307,901 sales daily and the Mail 2,378,428 - it seems unlikely that the Mail is as unruffled as it claims. The more ebullient Morgan has more to offer about what is really going on "behind the frivolity".
What is taking place between the papers, he says, is a battle for a new generation of women readers, the key to the Mail's past success and the key both papers believe to be the future.
That a contest is underway seems obvious. Some weeks ago the Mirror launched a new women's magazine with the title M. The Mail brought out a spoiler in the same week. The appearance of the two supplements emphasised the keen rivalry between two papers, which have traditionally regarded themselves as dominating very different segments of the market, one very firmly centred in Middle England, the other in working-class estates across the land.
The Mirror saw the controversy around Posh's weight as an ideal opportunity to further its ambition to become the modern young woman's paper of choice. While Morgan recognises that the Mail's success owes everything to its early recognition of the importance of women readers, he argues it is too "fuddy duddy" to win over the next generation.
Hence The Mirror's assertion last week that the Mail's attacks on seven- and-a-half stone, 5ft 6ins Posh betrayed an anti-female bias. For, Morgan argues, the question is not really whether Posh has an eating disorder but the Mail's treatment of the story. What damage would the headline "Skeletal Spice" do if she was actually anorexic? he asks. "That was Posh's point to me," he adds.
So is The Mirror's strategy to win over women readers with a kinder, more sensitive coverage? For Morgan, last week was about more than that. There was a class dimension to the dispute. The Mail's animosity towards both Beckhams shows just how out of touch and snobbish it is, he says. The Mirror, by contrast, is "backing the Beckhams", great "British success stories".
Could The Mirror also be acting as hand maiden to the Labour Party which is currently involved in its own war with the Daily Mail? New Labour, tired by the endless stream of knocking stories appearing in the Mail, recently launched its own paper - the Daily Mail Monitor - which aims to expose the Mail's inaccuracies and bias. Morgan says there is no joint campaign against the Daily Mail but that he shares New Labour's contempt for the "appalling racist, sexist, homophobic misogynist rag".
So, even accepting the huge part Dacre's own prejudices are believed to play in the general tone of the Daily Mail, did Morgan demean the noble profession with the publication of the Fatso Dacre picture? Was it not a step too far, and a touch childish?
Morgan is unrepentant. He says he simply shone a light on "an old man responsible for trying to destroy a young women". Dacre suffered only one injustice. Despite the sumo wrestler portrayal in The Mirror, Morgan admits Dacre is "rather svelte" in real life.