From the late 1960s my family spent every weekend and most of the summer holidays axle-deep in a muddy field surrounded by 50 or so other Dormobiles and Commer Highwaymen. Despite the rather raffish brand names of our vehicles, we members of the Motor Caravanning Club of Great Britain (South East Division) were actually a rather stately crew. There was Commander Rees, who had seen distinguished service during the "last war", as older people still called it, and whose caravan was still painted in camouflage. There was Rick, a postman from Crawley who, to designate his status as our unofficial master of ceremonies, always wore a fez. There was us, a preternaturally quiet and well-behaved little family in shorts who barely said anything except to ask politely the way to the Elson disposal unit. And then there were the Misses Buddicom, a pair of elderly sisters whose main interest, as far as my eight-year-old self was concerned, was that they shared their temporary home with two cats which were able to come and go as they pleased thanks to a special step-ladder with tiny paw-sized rungs propped against the open window of their caravan's cab.

The Misses Buddicom didn't mix much, but then none of us did. Although still I was able to catch glimpses of the Misses Buddicom as they went about their caravanning duties, changing their Calor gas bottles, cleaning the windscreen and repositioning the elfin step-ladder for the cats. There was Miss Buddicom herself (as the elder, she got the privilege of the more formal title), a tiny, almost spherical woman who seemed a hundred but was, I know now, in her early 70s. Since she couldn't drive, her job was to keep house, as it were, in the "Aardvark", the custom-built caravan that she had painstakingly designed herself. The choice of name, she once explained briskly to my parents, was so that, whenever there was an alphabetical list drawn up of all the motor caravans of Great Britain, "the Aardvark" would always come first, a state of affairs which, she implied, was entirely in the natural order of things.

The slightly younger sister, Miss Guiny (Guinever), was tall and thin and silent. Her job was to drive the Aardvark every weekend from the sisters' home in Bognor Regis to wherever the rally was gathering that weekend - Hastings, Dover, Chessington (we were not what you'd call roamers). After that, Miss Guiny's duties seem to have been over, since I never remember her venturing outside the caravan until it was Sunday afternoon and time to call in the cats, unhook the Calor gas, before clambering into the cab to drive home again.

For nearly 10 years or so, the Misses Buddicom were part of the wallpaper of my life. But then, one day in 1974, my parents had some rather strange news. It seemed that Miss Buddicom had written a book. It wasn't, to my disappointment, about cats, a subject on which I knew she had published some rhyming verse. It was about George Orwell, the man who had written Animal Farm, which we had just done at school. Apparently Miss Buddicom had been Orwell's girlfriend!

It was hard to imagine the entirely round Miss B stepping out with Orwell, who I knew from the photograph on his book jacket was extremely thin. It was, in truth, hard to imagine Miss B having a boyfriend at all, since I knew from the example of my aunts that ladies of that generation - born around the beginning of the century - couldn't get husbands because all the men had been killed in "the Great War". So they had to grow moustaches and live with their sisters, just like Miss Buddicom did with Miss Guiny.

It wasn't until I was in my late teens, and had long shaken the dust of caravanning from my feet, that I actually read Jacintha - for that turned out to be her first name - Buddicom's Eric & Us. Growing up as neighbours in Shiplake during the early 20th century, Jacintha and Eric Blair (better known to the world as George Orwell) had been companionable chums who liked to read and write poetry and talk about the intellectual adventures they would have when both went up to Oxford (which, as it turned out, neither did). Eric, Jacintha admitted in her book, may well have had a bit of a crush on her - he certainly wrote her quite a bit of bad poetry in which he compared their situation to that of Romeo and Juliet. But the fact that he was younger put paid to any romance: "The two years between a girl of 17 and a boy of 15, as a beginning, are just the wrong two years."

Eric & Us has just been republished, with a new postscript by Dione Venables. And what a complex book it turns out, on rereading, to be. For all its gentle evocation of a shared upper-middle-class Georgian childhood spent on the Thames riverbank, it is clear that Jacintha Buddicom is really rather cross. What she's cross about specifically is the way that scholars (there were no biographers at this point, because Sonia Orwell was still ferociously in charge of the Orwell estate) have insisted on seeing Orwell as a lonely, sickly, impoverished and thoroughly miserable young boy. So Miss Buddicom, who was actually there and so should jolly well know, has decided to put the record straight.

She explains that she first met Eric in 1914 when he was standing on his head in a field at the bottom of the Buddicoms' garden. When asked why, he replied, "You are noticed more if you stand on your head than if you are right way up", which, as Miss Buddicom rightly points out, is hardly the reasoning of a shy child. From this resoundingly upbeat start, Buddicom sets out to show a young boy who was hale and hearty and, above all, popular. For every example of Eric sitting thoughtfully with a book, she gives three of him striding round the fields with her brother taking potshots at rabbits. He's not thin, she insists, but rather strapping, with a big, happy moon-face, and she's dug out some old family photographs to prove it.

The inconvenient fact that much of the evidence for Blair's unhappy childhood came from the man himself, writing in middle age, is a minor epistemological problem for Miss Buddicom. Seizing by the scruff of its neck "Such, Such Were the Joys", the essay Orwell wrote in 1947 about his miserable time at prep school, Miss Buddicom gives it a good shake and shows that it's all a lot of poppycock: "I can guarantee that the 'I' of 'Such Such Were the Joys' is quite unrecognisable as Eric when we knew him then." And to prove it she submits each of his claims to forensic examination. He says, for instance, that he smelt. "If he really had smelt I, for one, would never have associated with him." He says that he was made to feel a failure. Nonsense! He got a scholarship to both Eton and Wellington and everyone was jolly, jolly pleased. He says he was ugly. Well, says Miss Buddicom, she knows for a fact that Eric "had no homosexual tendencies" (otherwise her brother would have said something), so that probably explains why no one at St Cyprian's made a special pet of him. And a good thing too.

What immediately becomes apparent on rereading Eric & Us is that Jacintha Buddicom felt horribly betrayed by the way that the boy with whom she had shared her genteel, bookish childhood had grown up to denounce so much of what she held dear. The Road to Wigan Pier, to her mind, was depressing, while Homage to Catalonia was just plain wicked: "It is impertinence for independent members of a different nationality to interfere with the internal affairs of a country not their own." The novels were hardly any better: "If only one of them could have had, if not a happy, at least an encouraging ending." If at times Miss Buddicom's lament seems parodic of a certain kind of energetic Middle Englandism - you almost expect her to suggest that a few well-timed weekends in the Aardvark would have steered Eric away from what she sees as his morbid obsession with tramps - it is also painfully real.

The young couple lost touch shortly after Eric started work in Burma and, incredibly, it was not until a few months before his death in 1950 that Jacintha realised that the moon-faced boy who liked to stand on his head was none other than George Orwell, perhaps the most celebrated British author of the mid-20th century. They exchanged a few letters, in which the dying Blair seemed touchingly keen to introduce Jacintha to his young adopted son. But it was all too late, and Jacintha was left to try and piece together the journey of the last 40 years which had taken the soul mate of her youth on such an extraordinary tangent.

And there the sad little story of Eric & Us, a book which feels as if it has been written to an agenda so painfully submerged that the author herself is barely aware of it, might have ended. It would have taken up its place as a dusty curio, known only to committed Orwellians who, while they might occasionally glance at Miss Buddicom's account to fill in the odd early date, would have seen it as little more than the usual lament of a childhood friend who has been left behind in the glorious, choppy wake of a Great Man.

But Venables's postscript changes all that. Venables is the Buddicoms' first cousin, and was left the copyright to Eric & Us, as well as 57 crates of family letters. From these she made the shocking discovery that, in 1921, Eric had tried to rape Jacintha. Previously the young couple had kissed, but now, during a late summer walk, he had wanted more. At only five feet to his six feet and four inches, Jacintha had shouted, screamed and kicked before running home with a torn skirt and bruised hip. It was "this" rather than any gradual parting of the ways that explains why Jacintha broke off all contact with her childhood friend, never to learn that he had transformed himself into George Orwell.

Venables believes that the attempted "rape", which, in truth, sounds more like a botched seduction, may also explain the sad, desperate things that happened next. She reveals for the first time that, in 1927, Jacintha gave birth to a daughter as a result of an affair gone wrong, and was obliged to let her childless aunt adopt the baby. When Eric returned that year on leave from Burma, he interpreted Jacintha's absence from the Buddicom family home as evidence that she was still angry with him (in fact, she was spending six painful months in seclusion). Any chance of picking up where they had left off, perhaps even marrying, had now gone for good. From that point, both of them seemed to give up any hope of forming a nurturing relationship. Eric turned to Burmese prostitutes and Jacintha to a 30-year affair with a Labour peer.

Jacintha Buddicom's missing child may also explain why, after making contact by letter with Eric in 1949, she dragged her feet about a face-to-face meeting. He said he wanted to talk to her urgently about Richard, his adopted son, and Jacintha seems to have been terrified that she would be asked to bring up her former sweetheart's child 25 years after having been forced to give up her own. She may even have thought, Venables speculates, that Eric would ask her to become his wife. After several weeks of dithering and dawdling, Jacintha received the half-welcome news that he had conducted a deathbed marriage to Sonia Brownell instead.

Jacintha Buddicom came from an age and class that did not make a fuss. Admirable though that is in one way, it means that her churning rage and hurt were forced to run underground. This explains the curiously coded and uneven quality of Eric & Us, the sense one has of not being quite the reader to whom the book is addressed. It also accounts for a desperate moment in 1974, during an interview for CBC, when Buddicom was asked about the events she had described in Eric & Us. Under gentle questioning from the interviewer as to whether there was perhaps something left unresolved about her relationship with Eric Blair, the usually imperturbable woman, stalwart skipper of the "Aardvark", broke down and sobbed.

· Eric & Us by Jacintha Buddicom is republished by Finlay Publisher, price £8.50