The ruling that Dan Brown's book The Da Vinci Code did not breach copyright law is good news for authors, according to a Warwickshire lawyer.

But Laurie Heizler, of Leamington-based Wright Hassall, has still warned writers to be on their guard if they are using theories or ideas from other people's works. The law protects authors if they wish to use historic themes or scenarios and give them fictional treatment providing text is not substantially copied.

In this case, the judgement found that Brown's publishers had not breached copyright because the author had merely used the ideas of Michael Baigent's and Richard Leigh's The Holy Blood and The Holy Grail in The Da Vinci Code (both right).

Mr Heizler said: "The judgement is very good news for authors such as Brown who might wish to create a fictional treatment of a real or speculative set of historical facts, themes and ideas.

"But the impact is not revolutionary as the principle that ideas are not protected by copyright is upheld.

"However, there has to be a word of warning. An idea or a theme is an ambiguous concept and if there is sufficient originality and substance in a format there can still be a breach of copyright.

"You see this very often with game show formats which are largely considered to be protected by copyright. A recent case upset the classical music recording industry by stating that copyright can exist in modern arrangements of 17th century compositions."