Who's laughing now?

The Earl of Macclesfield has found a golden lining to his cloud. Although due to be evicted next year from Shirburn Castle, Oxfordshire, his ancestral home since 1716, in one of the most bitter family quarrels ever to split the British aristocracy, he has recently become one of those rare artistocrats: a man suddenly worth many millions.

His totally unknown family library, which in November reaches the fourth of what will be up to 13 auctions at Sotheby's, has turned out to be one of the most important ever sold - comparable, though very different, to the famed book collections of the Duke of Devonshire at Chatsworth, the Duke of Roxburghe at St James's Square and Earl Spencer at Althorp.

When all 20,000-plus volumes reach the auction block, the 62-year-old Oxford-educated peer will have pocketed more than £20 million. On top of that, he has a £6.37 million sale behind him to Cambridge University in 2000.

The extraordinary story of the charismatic lord, his new-found wealth and the fury of his relatives is made even more poignant given that for most of his life, Macclesfield has been unable to repair the roof or the moat at Shirburn - a Grade I-listed, 60-room, fairytale castle easily mistaken for Bodiam and as deeply unknown to the public as his hidden library.

Now his multi-million pound gift from dusty corners of his castle might enable his lordship to buy out his "vile" relations and live happily ever after.

Because, for all the quarrelling, there is no dispute that the contents of 14th-century Shirburn Castle belong 100 per cent to the earl - covenanted to him by his grandfather in 1967 on his wedding day.

They include, with the books, pictures headed by a 1730 Hogarth three-quarter-length portrait of his forebear, the 2nd Earl. If that is in the same extraordinary condition as the books, his lordship could add another £4 million to his pile.

The walls, the fabric, the moat and the 2,250 verdant acres on the Chiltern Hills that surround Shirburn may be the property of Beechcroft Estates, the family company in which the earl owns just 25 per cent of the equity - his estranged brother, uncle and nephew own the rest - but the treasure chest is his.

It must have the family, known none too genially by the earl as "the buggers", hopping mad. According to the Countess of Macclesfield, "the families haven't had a civil conversation for years". The heart of the matter is this: who's the king of the castle?

Their quarrel centres on attempts, stretching back over 30 years and now finally successful, by the earl's uncle Jocelyn (now 83), Jocelyn's son, Robert, and his younger brother David, to evict him from Shirburn, which has been his home since 1962. The castle is company-owned, and Jocelyn and David have a majority of the shares.

Jocelyn, Robert and David tried for two decades to evict the present earl's father before nailing the 9th Earl in the High Court last year. Relations between the two sides, declared Mr Justice Lewison modestly, were based on "palpable dislike".

But now Sotheby's has come to the rescue.

Shirburn is not the first English house to discover in the 20th century that what is inside is significantly more valuable than what's outdoors. Blenheim, Chatsworth, Warwick, Bowood, Eaton Hall, Alnwick, Leeds - the list is endless, and an exact reversal of values before 1882, when the land was what mattered, not art and very rarely indeed the books.

The earl is suddenly so rich after being poor that, approximately two years from now, he will be close to having the money - between £ 30 million and £40 million - needed to buy out the rest of his family and to reinstate Shirburn as the property of himself and his heirs. If, of course, he wants to. Does he?

"Oh, sadly, no," he replied immediately when I asked him. "It's a family fight. It cannot happen."

Why on earth not? "It will cost a fortune to buy out everyone else. It's a very valuable estate."

But, beyond doubt, he will now be able to afford to gain 51 per cent of Beechcroft Estates and take control? "Oh no. That's not a solution. I'd still be fighting the other buggers."

But with an uncle well into his eighties and a brother who is openly sorrowful about the whole ghastly quarrel, surely the children aren't going to perpetuate the battles of their parents?

"You're wrong," the earl replies tersely. "It's not on.

It would be fighting for ever. The children of Jocelyn [his uncle] are even more committed to this than he is. They see the castle as their future. A solution is just not possible with the mindset of the people I'm dealing with. I'm 61. I've had enough. There's too much water under the bridge for any recovery. I'm out."

The earl, his American-born second wife, Sandy, and his daughters - Ladies Tanya, Katharine and Marian, by his first marriage to another American, Cleone Wheaton-Smith - are presently under orders from Mr Justice Lewison to leave Shirburn Castle by August 2005. There is an appeal pending against that judgment from July 2003, but it relates only to costs.

Lord Macclesfield, giving up the fight, maintains he is "destined" to go. When he does so, he will pick up perhaps another £8 million as Beechcroft Estates buys out his 25 per cent equity.

His new home, however, will not be far away: just 10 miles up the road from Watlington, just off the Shirburn estate. The house is "most beautiful", he says, and will presumably have some of the earl's new millions lavished on it.

It sounds, I tell him, that since the Lewison judgment, he has finally obtained the emotional detachment to leave Shirburn and all it stands for and move on with his life.

"Yes, I have," he announces with decision. "My attachment to it is all gone. I'm detached, all right. You get there in the end. That's what quarrels and litigation do to you." The earl has no idea what will happen to Shirburn next: his uncle and his brother, who do not talk to the press, have not enlightened him. He assumes commercial intent, not least because the High Court judge certified that 50,000 visitors a year are needed to service repairs to the Castle.

In the same breath, the earl declares 50,000 visitors a year, even to the hidden beauty of Shirburn, is impossible. He believes an infinitely more plausible prospect is "sale to an Arab".

Is Shirburn viable no other way? "I'm arrogant enough to believe that I could have made it work if I'd had the freedom to do so." By efficiency, or by a brilliant idea? "Efficiency."

But his voice tails off. Shirburn has been "a lose-lose situation" since Lord Macclesfield's grandfather, the 7th Earl, dreamed up in 1922 a plan to save his house from income and capital taxes. It was to take it out of entail within the family and put it in company ownership, with differing members of the family owning partshares.

Perhaps for good reason, the "Beechcroft Estates solution" to saving the English country house has not proved widely popular among landowners in modern times.

"The few who've adopted this model have tried two forms - turning the house into a charity, with the family paying rent; or turning the house commercial, with the family moving out," says Christopher Sokol, tax barrister at Lincoln's Inn. "Its disadvantages are that no one has final control, which can lead to disputes; and it's fairly pointless if the family sticks to primogeniture."

The one advantage for the individuals in the model is that on death, their "estate" is only that share of the property of which they own the equity - in Lord Macclesfield's case, 25 per cent.

Meanwhile, Sotheby's is piling up the millions for the earl. At its ninelot, £2.27 million auction in June, the Macclesfields sat in seats of honour as the senior book dealers of the UK, America, France, Italy and Germany bid up their books to 12 times the estimate.

Prime among them was the rediscovered Macclesfield Psalter, a vellum manuscript with superb illuminations, probably made in Suffolk circa 1320-30 by an unidentified English hand of genius - the same that decorated the Gorleston Psalter in the British Museum. It sold for £1,685,600, twice Sotheby's expectation.

"Lord Macclesfield is a man with a limited range of facial emotion," reported an eye-witness at the auction. "Lady Macclesfield wore an expression which indicated that if she had a choice between a dusty old book and £1.5 million in the bank, there was no choice. She smiled more broadly than the Cheshire cat."

The trophy of trophies in November, at the auction of science books by authors D to H, will be Galileo's Sidereus Nuncius, in which he announced his discovery of the moons of Jupiter. It is estimated at £250,000-£350,000. Books by Isaac Newton are to come in 2005. Sotheby's is keeping details up its sleeve.

Their survival, it seems, is handsomely due to poverty at Shirburn Castle. The library did not enjoy electricity until quite recently. As a result, it has avoided the ravages of temperature ups and downs from central heating and excessive exposure to light. "The library was cold but not damp," says Sotheby's book expert Stephen Roe. " It was untouched, just dusted occasionally."

Even poverty, then, can have a silver lining.