Sir Martin Sorrell’s WPP reported a 12% rise in pre-tax profits to £1.45bn for 2014 but warned of political and economic uncertainties to come.

WPP, the world’s biggest advertising company, reported strong growth in all its regions, including Britain and North America, last year and said it had made a good start to 2015.

Headline profit before tax topped £1.5bn for the first time, up 3.7%.

Revenues grew 4.6% to £11.53bn in 2014, broadly in line with forecasts, in its preliminary results published on Monday.

The group, which includes the advertising agencies JWT and Ogilvy & Mather, said like-for-like revenues were up 6.7% in January this year and like-for-like net sales up 3.9%.

But the group warned of continued uncertainty in Europe and the “litany of woes” in the Middle East in a variety of factors – or “grey swans” that might affect its future performance.

It said the result of the UK general election was “increasingly uncertain” and “may crimp the strong UK economic recovery, which equals or even exceeds the US strength, albeit relatively.

“If the Conservatives win outright (unlikely?) or lead a coalition or even form a minority government, there will be a referendum on the EU in 2016 or 2017, which will cause significant uncertainty.

“If Labour wins outright (also unlikely?), or leads a coalition (more likely with the SNP?) or forms a minority government, it will win partly on a ‘bashing business’ manifesto, which may resonate at the ballot box.

“Either way, the UK economy may slip into the political cycle again, with austerity in the early part of the five-year cycle to deal with the continuing budget deficit and better times around the next election in five years’ time (or earlier?) – just like the current chancellor has done so brilliantly for the coalition, in their first term.”