On Wednesday, the belligerents - Charles Moore, editor of The Daily Telegraph, and Sir David English, editor-in-chief of The Daily Mail - will come face- to-face at the offices of the Press Complaints Commission, of which Sir David is chairman. In those gentlemanly surroundings, they may manage to exchange a civil greeting. But the atmosphere promises to be distinctly chilly.
The printed exchanges have been heated. Wednesday's leader in The Telegraph said: "To have such people [as Sir David English] deliberating on ethics is like inviting Gerry Adams to chair a committee verifying the IRA ceasefire". In Friday's Daily Mail, crowing about its own soaring circulation and The Telegraph's commercial problems, one media analyst said: "The real problem is that The Telegraph is edited by a dilettante who seems more concerned with venting his spleen on the airwaves than actually editing his paper. It's a disgusting abuse of his position."
The quarrel began last Tuesday in the wake of Earl Spencer's attack on press intrusion at the funeral of his sister, Diana, Princess of Wales. Mr Moore fired the first shot and, after a short pause, Sir David responded. That, in the normal course of things, should have been that. But as the week went on, the sparring continued, and passions still show no sign of subsiding. This, it seems, is something more than a run-of-the-mill spat between rival newspapers.
The catalyst was a pledge by a number of tabloids last Monday that they would no longer purchase the wares of "paparazzi" photographers. In a self-righteous headline, The Daily Mail announced: "Mail leads the way in banning paparazzi pictures."
After a week of watching the tabloids whip themselves into a frenzy over the Princess's death, the cerebral Mr Moore saw red. In his office in Canary Wharf, he penned a lengthy, unsigned leader for Tuesday's Telegraph in which he thundered against their "philosophy of intrusion". He named The Mail - under its proprietor, Lord Rothermere, and his "Grand Vizier", Sir David - as the worst offender because of its pretensions to be a serious- minded newspaper.
Referring to an article that described the Prince of Wales weeping "bitter tears of guilt" during a walk alone on the moors at Balmoral, Mr Moore wrote: "A paper which proclaims its devotion to `family values' was doing what no one who really cares for any family would do - inventing feelings, hinting at blame, prying, with a horrible, pharisaical precision, into the most tragic aspects of other people's lives."
That morning, during a debate on privacy on Radio 4's Today programme, he repeated those sentiments and accused The Mail of "prying in the most disgusting way into private family life and now into private family grief". Sir David - who doubles as chairman of Associated Newspapers, which owns The Mail - entered the fray, telling Today listeners that Mr Moore wanted to undermine The Mail because it had stolen so many of his readers.
Thus the stage was set for a joust between two newspapers that vie to articulate the values of Middle England, and between two men who are absolute polar opposites. In the blue corner, Charles Moore, high-minded Old Etonian, right-wing Conservative, Catholic convert, defender of Queen and country. In the other blue corner - for he is equally wedded to Tory ideology - Sir David English, legendary former Mail editor, talented newspaper technician, Thatcherite knight, ruthless manager with a reputation for never losing a battle.
Initially, The Mail kept its powder dry, having decided, according to insiders at the Associated offices in Kensington, against dignifying Mr Moore's outburst with a detailed response. At The Telegraph's office at Canary Wharf, word went round that the editor was on a crusade and that senior executives expected staff to rally to the cause.
On Wednesday, The Telegraph ran its David-English-as-Gerry-Adams leader. The Grand Vizier promptly picked up the gauntlet. In a letter published in The Telegraph the following day, Sir David condemned Mr Moore's "scurrilous" attack as "a cynical exercise ... motivated by commercial fear and envy".
By now, Mr Moore had the bit between his teeth. On Friday, he wheeled out Stephen Glover, the media pundit, to deplore The Mail's "constant critique" of Diana and its "undoubtedly sometimes nasty" methods. The Telegraph that day was full of letters to gladden an editor's heart. "Sir David English's attempts to justify his deplorable rag will cut no ice with readers of a proper newspaper," stormed one. Richard Kay, The Mail's Royal correspondent, also wrote in, defending his story about the Prince at Balmoral.
On Saturday, in what should have been the showdown, The Telegraph fired its biggest gun. In a speech to the Spruce Meadows Round Table in Calgary - faithfully reported by The Telegraph - Conrad Black, the newspaper's combative Canadian owner, compared Sir David's chairmanship of the PCC with having "Al Capone as head of a commission to investigate organised crime". The same day, Sir David accused The Telegraph in a second letter of "a calumny of lies, black propaganda and inaccuracies".
This, though, is not the end of the story. Mr Moore, who wrote an open letter to Sir David in Saturday's paper, still has plenty of fire in his belly. "This is not some game; we mean business," he told The Independent at the weekend. "If we can't take on intrusion now, when can we?" Sir David, for his part, is busy assembling examples of allegedly intrusive reporting and paparazzi photographs that have appeared in The Telegraph, for an article he plans to offer for publication in that paper.
Staff at The Telegraph, meanwhile, are bemused by their editor's evangelical fervour and the timing of his campaign. Fresh from a costly price war with The Times, its profits slashed by an ill-conceived cut-price subscription scheme, the newspaper seems poorly placed to pick a fight with the hugely successful and self-confident Mail.
Although the two papers inhabit similar territory in the middle market, few at Canary Wharf think that Mr Moore is driven by commercial considerations. He genuinely feels, they say, that he is on a mission. He may also believe that he has identified a way to escape the ideological vacuum in which The Telegraph has been floundering since the general election. With the Conservatives in disarray and Labour still enjoying a honeymoon, the paper desperately needs a new outlet for its energies.
His readers, though, must be mystified. To those outside the media, such feuds are of limited interest, and it is no accident that this one has been played out almost exclusively in the pages of The Telegraph. The only hint of the row to have appeared in The Mail was the triumphalist piece on Friday which reported a million-plus circulation lead over The Telegraph, adding mischievously that "industry observers" were concerned about The Telegraph's "rapidly diminishing appeal in a modern world".
Sir David, whose response to his public vilification has been strikingly restrained, said on Saturday: "I hope Charles Moore keeps this up. How long can an editor bore his readers before they rise up in manic rebellion?"
More seriously, he is concerned that the affair may rebound badly on the industry. Lord Wakeham, the PCC chairman, is understood to regard it as unhelpful at a time when self-regulation is once again under scrutiny. He is thought to have assured Sir David that he retains his confidence as committee chairman.
Both Mr Moore and Sir David insist that there is no personal animosity between them. However robustly their dispute may be expressed, it is about shifting perceptions of acceptable professional conduct. Perhaps they should both take a leaf out of The Mail's house manual of 45 years ago, which counselled journalists to consider the following dictum: "Would you write the story if it was about the proprietor or his family?" As a letter writer to The Times suggested last week, this could apply equally well nowadays as a general rule of common decencyn