Probably one of the most famous lines we've ever written – although a lot of its success had to do with the fact that it came out of the mouth of Jennifer Aniston at the height of her Friends success.

We were desperate to do something interesting for L'Oreal – it was a luxury brand that was badly underselling itself with lifeless, poorly dubbed US – import films.

So we convinced the UK client to strike out on his own and sign up the owner of the "Rachel-cut" for a European-only campaign.

The series of commercials we shot with Jennifer turned around the fortunes of L'Oreal UK and proved that with a little bit of proper acting talent you can transform celebrity beauty testimonials into something entertaining and meaningful.

Suddenly with an actress, rather than a supermodel, delivering our lines we were able to get every line in two takes, allowing us to shoot enough material for six spots, not one.

We knew we had to have the obligatory scientific message in the middle of the film, but rather than just cut and paste it in, we decided to write Jennifer's script so that it acknowledged its existence in the middle of the film – and even dared to make fun of it.

That one line transformed L'Oreal into a brand with the heart and humour to laugh at itself.

We later heard that the L'Oreal scientists in the main labs outside Paris had got the line printed up on t-shirts and would begin every lecture theatre presentation of their latest formula breakthrough with those immortal words.