Sir Martin Sorrell, the WPP chief executive, has said he believes that Netflix will have to look at introducing advertising to become profitable.

WPP, the world’s largest marketing services company, manages $78bn a year in advertising spend on behalf of advertisers.

Sorrell, speaking via video link at the FT Digital Media conference in London, was asked about the impact of ad-free online services such as Netflix and HBO Now built on the back of heavy investment in content.

“We make content [too],” said Sorrell. “We invest in Vice [Media], we invest in [House of Cards producer] Media Rights Capital. We are investing in content heavily. The last time I checked, while the Netflix model is a powerful one it hasn’t achieved that old-fashioned thing called profitability.”