The term "carbon intensity" can be used in adverts promoting firms' green credentials, as long as it is clearly defined or equated to absolute carbon reductions, according to a new ruling from the UK's advertising watchdog.

The adjudication came in response to complaints received by the Advertising Standards Authority (ASA) over a TV advert from energy giant EDF which claimed the company aimed to "reduce the carbon intensity of CO2 emissions from their electricity productions by 60 per cent". The voiceover was accompanied by on-screen text claiming "aims based on improvements to EDF Energy's 2006 performance and is subject to change in the event of matters beyond EDF Energy's reasonable control".

The advert resulted in five complaints from viewers challenging whether the 60 per cent claim was misleading, as most viewers would not understand the term carbon intensity and would believe EDF intended to cut absolute emissions by 60 per cent.

In its response EDF argued that carbon intensity, whereby energy firms measure their emissions per unit of electricity, was an increasingly popular form of measurement in the energy sector that allowed for better comparison between rival operators and provided firms with the ability to track their performance, even if demand for electricity increases, for example as a result of wider adoption of electric vehicles.

It also claimed that while terms such as carbon intensity might not yet be fully understood by everyone, that should not prevent it being used to raise awareness of the issues, adding that the EDF web site contained a full glossary of that and other terms that might be less well understood by their customers.

Furthermore, the company said that the advert had not attempted "to artificially inflate their commitment claim" and that its analysis could have reasonably justified the claim that it was aiming to cut carbon intensity by 67 per cent. As such, the company said it also expects absolute emission to fall by 61 per cent on 2006 levels by 2020.

Consequently, the ASA rejected the complaints on the grounds that viewers were unlikely to be misled regardless of how they interpreted the claim.

A spokeswoman for the ASA said that the ruling would provide a precedent for advertisers, observing that the term carbon intensity could be reasonably used in adverts as long as it is clearly defined or used in a way where claims relating to targets can also be applied to absolute carbon reduction goals.