Reported revenue from the first three months of the year was £3.59bn, up 0.9% compared with Q1 2018, but revenue less pass-through costs for the quarter was £2.93bn, down 0.7% on a reported basis and -2.8% like-for-like.

Like-for-like revenue less pass-through costs was down 8.5% in North America in the first quarter due to losses in automotive, pharmaceutical and FMCG clients, while net sales also declined slightly in the UK and Western Continental Europe.

Asia Pacific, Latin America, Africa and the Middle East, and Central and Eastern Europe was the strongest performing region for WPP, with net sales up 2.3%.

Average net debt dropped to £4.16bn from £4.87bn in the first quarter of 2018, and the company has not changed its expectations for the full year.

The company said its ongoing sale of Kantar is "progressing well, in line with our expectations" with the business attracting interest from "high-quality potential partners", but did not offer any further detail.

WPP chief executive Mark Read (pictured) said: "As anticipated, our first quarter trading update reflects the impact of certain significant client losses in 2018, in particular in the United States. Although we face a challenging year, especially in the first half, I am encouraged by how well our people, agencies and clients are responding to our new strategic direction. 

"As we have said before, it will take time to address the company’s legacy issues, but we are committed to taking all the actions necessary to position WPP for future success."