Shares in WPP slumped more than 6 per cent on Friday morning after the world’s biggest advertising company cut its sales forecast for the year citing an ultra-competitive market.

The group said that clients “face challenging top line growth opportunities and uncertainties” and that “given this macro-economic background […] clients are generally grinding it out in a highly competitive ground game”.

WPP, which employs more than 205,000 people across more than 100 countries, reported 2016 net sales growth of 3.1 per cent, which was broadly in line with expectations, but it said that 2017 had started more sluggishly, prompting the company to cut its target to around 2 per cent growth for the year ahead, “given continued tepid economic growth”.

“WPP is a hugely successful business, but it is feeling the effect of slower growth in the UK and USA, where clients are spending less,” said Danny Cox, a financial planner at Hargreaves Lansdown.

“When you are the size of WPP, with revenues of £14bn a year, you can’t but notice the broader state of the economy,” he added.

Annual pre-tax profits hit £1.9bn in 2016, up 26 per cent on the previous year.