In the recycled world of news journalism, one question crops up repeatedly.

How much of an article can be legitimately copied without the copyright owner’s permission?

The issue has become more important since the arrival of the internet, with its massive scope for copying.

In UK law, the short answer has three elements.

First, part of a copyright work can be used without permission so long it does not amount to “a substantial part”.

Second, a copyright work can be used without permission so long as the usage amounts to “fair dealing” for the purpose of criticism or review, is accompanied by sufficient acknowledgement, and the work has previously been made available to the public.

Third, a copyright work (other than a photograph) can be used without permission if the usage amounts to “fair dealing” for the purpose of reporting current events, with sufficient acknowledgement.

But that answer is deceptively simple. The phrases “substantial part” and “fair dealing” offer troublesome scope for legal argument.

It’s clear from court rulings that assessing whether “a substantial part” has been used is essentially a matter of impression and degree. That’s not much help if you want certainty at the outset of litigation.

Unfortunately, it’s not possible to generalise that use of a certain percentage of a copyright work would not be “substantial”.

More important than quantity are the quality, importance, and commercial value of what has been taken – and those are elastic concepts.

In the media context where criticism, review, and news reporting are obviously commonplace, the “fair dealing” defence adds a further layer of uncertainty over and above any arguments about what is “a substantial part”.

As with the elastic concept of “substantial part”, the phrase “fair dealing” also escapes easy definition. Again, the extent of the use and the importance of what has been taken are key factors in the court’s assessment of fairness.

Other important considerations are whether the alleged infringing use competes with the copyright owner’s exploitation of the original work, and whether the original work has been published or not.

There’s a dearth of illustrative case law regarding print media on this aspect of copyright, but in an often-cited broadcasting case, British Satellite Broadcasting successfully defended an infringement claim by the BBC after BSB used clips, of 14 to 37 seconds in length, of the BBC’s footage of the World Cup finals.

BSB broadcast the clips several times in 24 hours. A court decided the usage was fair dealing for reporting current events.

Journalists often wonder whether hard-won quotes from their own, or a rival’s, exclusive interview can be legitimately recycled without permission.

A quote might be just a small part of an article, but qualitatively it could be very important in terms of value and the ingenuity and labour required to compile the piece. If a lengthy, valuable quote is copied in its entirety by a rival newspaper, that is arguably not “fair dealing”, even if the purpose is to report current affairs.

No doubt the Kent Messenger grappled with such issues recently when significant parts of its copyright interview with the wife of jailed comedy star Chris Langham were recycled the next day by national newspapers, triggering a letter of complaint.

The overriding practical consideration in these matters, however, is always costs.

It rarely makes commercial sense to sue for alleged copyright infringement if the costs of doing so will inevitably be disproportionate to the damages likely to be awarded to a successful claimant.