WPP’s Group M is Britain’s biggest media buyer.

On the Campaign website, Smith has been quoted as saying that while brands are likely to invest less as a result of the uncertainty related to Britain’s exit from the European Union, it will be "a difference of degree, not magnitude".

While he avoided offering a revised forecast for 2016 ad revenues on the basis that it would be speculative, he predicted that traditional media – print and TV – would likely take the biggest hit, as internet advertising continues to see forward momentum. 

"In the short run – say the next six months to a year – it is likely companies will invest less than if we had voted to remain," Smith was quoted as saying. "Job creation, wage growth and productivity will be lower than they would otherwise have been. This is a difference of degree, not magnitude.

"In the UK, print media trading has become increasingly short-term. TV trading has always been based on share, not volume, so TV market ‘visibility’ is poor in any case. Radio, out-of-home and cinema are much smaller and correspondingly more vulnerable to ad cancellation.

"Only digital media carry the forward momentum of ‘structural’ growth, meaning a strong prospect of above-average ad growth and thus market share gains independent of the economic cycle."