WPP, the world's biggest advertising company, said it had seen demand improve in January after strong trading in North America and China helped the British firm meet 2014 targets and lift its return to investors.

The British company, owner of the JWT and Ogilvy & Mather agencies, has outperformed its peers in recent years due to its wide geographical spread and strength in digital advertising, and said it expected this to continue in 2015.

Strong performances from its agencies in the United States, Britain and China, and an improvement in Western Europe, helped the firm post a 3.3 per cent rise in 2014 like-for-like net sales, with that measurement rising to 3.9 per cent in January.

Analysts welcomed the results, and WPP shares opened 1.2 per cent higher to add to the 14 per cent rise since the start of the year, although they noted that the full-year results marked a slowdown in the fourth quarter.

WPP, run by the high-profile British businessman Sir Martin Sorrell, said it had topped the industry's new business table for the third year in a row and said it expected solid growth in 2015 following a number of big contract wins.

WPP, which has more than 179,000 staff in 111 countries, raised its dividend 11.2 per cent, taking its pay-out ratio to 45 per cent from 42 per cent last year.

Sir Martin said the strongest growth had come in the travel, airlines and entertainment sectors while packaged goods companies remained under pressure as shoppers looked for cheaper deals for their consumer brands.

"The growth has been across the board," he said. "I was pleased with the recovery in western continental Europe. But the two areas that make the big difference are the US and China."

WPP said trading in Britain could slow down after the May 7 parliamentary election as which ever party wins will need to pay down the deficit.

The company will aim to buy back two to three per cent of its outstanding share capital.

WPP uses net sales as its main measurement, which differs from overall revenue due to the way it books some income, and on the like-for-like revenue basis more commonly used it outperformed its peers, with a 2014 figure of 8.2 per cent.

That compared with 5.7 per cent at Omnicom, the US advertising company, and a two per cent rise at France's Publicis.

"WPP remains a true global barometer, extracting gains from the economic pockets which are faring well, whilst also being mindful of the macro and geopolitical concerns which are yet to be resolved," said Richard Hunter, head of equities at Hargreaves Lansdown Stockbrokers.