Channel 4 is offering £1 million of free airtime for an advertising campaign which challenges the “stereotypes, objectification and sexualisation of women”.

Brands and agencies have been asked to come up with ideas which challenge the portrayal of women in adverts.

The announcement comes after Channel 4’s gender pay gap was revealed to be more than 10% above the national average, despite its workforce being comprised of 59% women.

Channel 4 chief executive Alex Mahon has called the 28.6% pay gap at the broadcaster “unacceptable”.

Studies have shown that women in adverts are mostly in their 20s, while men feature prominently into their 30s and 40s.

One in 10 female characters are shown in sexually revealing clothing and women are more likely to be in the kitchen, according to the research.

Channel 4’s campaign coincides with the #MeToo movement, the centenary of the date women first gained the right to vote, and recent controversy over the gender pay gap.

The broadcaster’s head of commercial marketing Matt Salmon said: “There are campaigns already on our screens which represent women in a positive and appropriate manner – but sadly there just aren’t enough of them.

“This year we’re looking for an ad that really stands out even from the positive ads we’ve seen before.

“We want a campaign that’s a beacon for the issue, an idea that calls out the challenges and makes a really positive statement to our audiences.”

The Channel 4 Diversity In Advertising Award is a commitment to help improve diversity in advertising each year until 2020.

It was won last year by Lloyds Bank, for a campaign focusing on mental health.