Section 16(3) of the Copyright, Designs and Patents Act 1988 (“the Act”) states “references in this Part to the doing of an act restricted by the copyright in a work are to the doing of it – (a) in relation to the work as a whole or any substantial part of it, and (b) either directly or indirectly and it is immaterial whether any intervening acts themselves infringe copyright.”
When considering whether a substantial part of a material has been copied the part of the copyright work which has been copied is what needs to be considered, not part of the copy as the test is a qualitative test not a quantitative test.
In the case of HRH Prince of Wales v Associated Newspapers Ltd  EWHC 522 the qualitative test was applied when the court decided copyright infringement had occurred when only parts of a journal were copied, but those parts were the parts which were of most interest to readers.
In the Nova Productions case the Court of Appeal held that where an amount is too general to a substantial part there would be no copyright infringement.
In The Da Vinci Code case the Court of Appeal held that where work fell on the side of being an idea rather than an expression there would be no copyright protection.
In the Designers Guild it was established that once copying had been established, the question was whether what was copied formed a substantial part of the original copyright work. The court will look at the similarities in the works when deciding whether their cumulative effect adds up to a substantial part of the copied work.
An inference of copying will be concluded where the similarities are enough to justify copying.
Where the part of the work copied is a very important part of the original work copyright infringement may occur (as the test for infringement is qualitative). However the work should be assessed as a whole and should not be split when assessing the whether or not the work has been copied.
Infringement can also occur indirectly where the author of a work copied the original through a re-creation of the original work.
In Infopaq International A/S v Danske Dagblades Forening, Case C-5/08 the ECJ said that words, considered in isolation could not be protecrted as they were not the intellectual creation of the author. However, there could be infringement if the elements reproduced (more than isolated words) were the expression of the intellectual creation of their author. In that case the judge stated:
“As regards the parts of a work….there is nothing in the Copyright Directive or any other relevant Directive indicating that those parts are to be treated any differently from the work as a whole. It follows that they are protected by copyright since, as such, they share the originality of the whole work… the various parts of a work thus enjoy protection under Article 2(a) of [the Copyright Directive], provided that they contain elements which are the expression of the intellectual creation of the author of the work.”