Britain's advertising watchdog has criticised cosmetics giant L'Oreal for a mascara commercial featuring actress Penelope Cruz that "exaggerated" the product's effects.

The Advertising Standards Authority said the company broke its rules and misled consumers by failing to make it clear that Cruz was wearing some fake individual lashes.

In the television commercial for L'Oreal Paris Telescopic mascara, Cruz stood on a terrace next to a telescope and said: "Imagine, lashes that could reach for the stars."

In a written ruling, the watchdog said the commercial "exaggerated the effect that could be achieved by using the mascara on natural lashes".

It ordered L'Oreal to make it clear in future adverts if models are wearing fake lashes.

The watchdog also criticised L'Oreal's claim of "60 percent longer lashes."

Some people might take that to mean their lashes would actually increase in length, rather than just look longer, the ASA said.

L'Oreal said it would comply with the ASA's orders.

"It is common industry practice to make use of some artificial lashes in order to ensure a consistent lash line under filming or shooting conditions," it said in a statement.