In the anonymous grey building near London’s Victoria station, a fax machine came to life on Tuesday lunchtime and began to spew out a long message. It went on for eight pages.

As senior staff at the Press Association (PA), the agency that serves as an information hotline to all of Britain’s news media, began to read the pages, it was clear this document would make waves.

Neatly set out in excoriating legal prose was nothing less than an inside account of Sir Paul McCartney’s failed marriage straight from the mouth of his wife, Heather Mills.

Leafing through the document, Teilo Colley, the duty news editor, saw that Mills had decided to make a down-and-dirty fight of the divorce. She was branding the national icon a drug taker, a drunk, a wife beater and a heartless brute who forced her to cook for him every night, sometimes while she was leaning against the oven on crutches and in agony.

McCartney had, in separate incidents, allegedly grabbed Mills’s neck and choked her, cut her arm and pushed her over a coffee table. He was possessive and petulant, the document suggested. It alleged that he had refused to let her get out of bed in the morning until he was ready, and had even ordered her not to breastfeed their daughter Beatrice because “they are my breasts”.

It was apparent that the former Beatle had also accused his wife of withholding sex from him and of embarrassing him in front of his friends and family with her belligerence.

Mills’s divorce document even described the couple’s final parting, in which a “staggering drunk” McCartney had come home demanding his dinner.

“That evening,” the document said, “the respondent (Mills) realised the marriage had irretrievably broken down and left, crawling on her hands and knees whilst dragging her wheelchair, crutches and basic personal possessions to the car.”

It was a potent, if bizarre, scenario and it galvanised tabloid newspapers that have long been feasting on the acrimonious breakdown of this high-profile marriage. The Daily Mail remade its front page for Wednesday’s edition and cleared a spread inside in order to accommodate every salacious detail.

The full ramifications of the fax are only now becoming apparent, however. Who sent it and why? Why were five pages missing from the document and what do they contain? At stake is the McCartney fortune, estimated at £825m. If one or other party were identified as having breached legal procedure — divorce documents are confidential — this could have repercussions when it comes to dividing up the estate.

Both sides have reacted similarly to the “security breach”.

Anthony Julius, the Mishcon de Reya partner who once secured a £17m divorce settlement for Diana, Princess of Wales, now represents Mills. He “went ballistic and was frothing with rage” when he was told about the leak, according to legal sources.

McCartney’s solicitor, Fiona Shackleton, who acted for the Prince of Wales during the royal split, has been equally dismayed by the turn of events.

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