With his long, lank hair and scruffy brown leather jacket, Richard Leigh did not look like a man with a spare million pounds in his pocket as he stood in a media scrum outside the High Court today.

After losing a copyright claim against Random House, the publishers of Dan Brown's The Da Vinci Code, Leigh, an American-born novelist and historian, and his colleague, Michael Baigent, have to make a down payment of £350,000 in the next 28 days. Even after that they will still owe £750,000 - plus their own costs, estimated in court at £800,000.

It was one of the most expensive mistakes in British legal history and Leigh, shell-shocked by the verdict, admitted that he had no idea how he would find the money. "I welcome any suggestions on that," he said.

Baigent and Leigh had accused Brown of stealing the "central themes" and "architecture" of their 1982 book, The Holy Blood and The Holy Grail - a claim totally rejected by Mr Justice Peter Smith. Both books posit the theory that Jesus Christ married and had children with Mary Magdalene, the bloodline continuing to this day.

Brown's 2003 bestseller has sold more than 40 million copies worldwide and added an extra half a million copies in a week when it came out in paperpack in the United States earlier this month, making him the world's best-paid author. Its US publishers have another five million copies on hand, waiting for the release of the $57 million Da Vinci film, starring Tom Hanks.

In contrast, Baigent's and Leigh's Holy Blood sold two million copies back in the 1980s and has sold perhaps 30,000 more on the back of the publicity from the High Court trial. Baigent, a New Zealander, did not attend today's verdict - he is travelling after the launch of his new book, The Jesus Papers: Exposing the Greatest Cover-Up in History, which has an initial print run of just 150,000.

After ordering the two men to meet 85 per cent of the costs of the publisher Random House, which coincidentally published both books, Mr Justice Smith asked how the two men were going to meet the bill. The answer was unclear, although their lawyer suggested that one of them might have to sell their house.

At that point, James Abraham, QC, for the publisher, jumped up to say that it had never been his client's intention to bankrupt the two writers, or force anyone to sell their house. How else, asked the judge, are they going to pay?

The pair wrote the Holy Blood book with a third writer, Henry Lincoln, an Englishman who now lives in New Zealand. Lincoln, a former scriptwriter for Z Cars and Dr Who, has been as disparaging as his colleagues about Brown's book, but refused to subscribe to their lawsuit and did not attend the High Court hearing.

After the verdict, Leigh said today that the pair had "lost on the letter of the law, but won on the spirit of the law" - a reference to the judge's finding that Brown had indeed copied from their book, but not in a way that infringed their copyright under UK law.

That partial victory might be some consolation, but in the meantime they have only a month to find the first £350,000 of their opponents' costs.

In his ruling, Mr Justice Smith referred to the testimony of Patrick Janson-Smith, a top literary agent who was involved in the publication of two books and who told the court that he had warned the claimants that they were "in danger of making fools of themselves".

The judge said that Mr Janson-Smith had suggested that Leigh had given the impression that the case was brought "for the purpose of extracting money in the expectation of settlement".

"I do not need to form a view as to that," he said. "All I will say is that if Mr Leigh believed that he demonstrated a folly which afflicts claimants from time to time.

"It is a very dangerous exercise to commence litigatoin in the hope that the other side will settle and make a payment. I rather suspect this will be driven home to Mr Leigh (if that was his thought) at the conclusion of this judgment."

During the case, the judge gained a reputation for bluff, but trenchant, humour from the bench. But his last joke was probably the most cutting.

After ordering the two writers to pay 85 per cent of their opponents' costs, the judge mentioned to their lawyer that the pair still had royalties coming in from their 1982 book. But he conceded: "It won't be anything like the figures we're talking about, unless your clients start going on roadshows and selling their books - or even Mr Leigh's new book."

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