Why is Sir Martin Sorrell worried when things are going well?

Pre-tax profits for 2014 rose 12 per cent to an unprecedented £1.45bn, on revenues that rose 4.6 per cent to £11.5bn. Encouragingly, the company also started January well, with like-for-like sales rising 6.7 per cent. The WPP share price is also riding high – at the time of writing it is almost three times the level it was four years ago, when we were still languishing in the post-financial meltdown hangover.

The giant group owns a host of agencies around the world, including long-established ones like Y&R, JWT and Ogilvy & Mather, as well as digital darlings like AKQA. It operates in well over 100 countries, from mature markets like the US to fast-growth regions such as China and various 'Next 11' nations (Indonesia, Mexico, South Korea, Philippines, Turkey and the like).

Sorrell, told the BBC there was some evidence things were picking up in the Eurozone. However, he said most global economic growth would continue to come from the US and China.

"We are seeing a little bit of an improvement [in the Eurozone] we saw a stronger Q4 and as we go into the first few months of this year January was stronger as well. So there are grounds for a little bit more optimism," he said.

But what really jumped out at me was the US numbers. America is the world’s largest advertising market – and is likely to remain so for a while yet – but it has, along with Europe, long been regarded as a mature market, from which relatively little growth can be extracted, particularly given the margin pressures most 'old world' ad agencies operate under these days.

The majority – £622m – of operating profits came from North America, with South America softening a bit (like-for-like sales growth slipped from 5.9 per cent in the first half of 2014 to 3.6 per cent in the second) and this demonstrates to me just how much WPP depends on the US and Canada. Fortunately, the US economy seems to be motoring along nicely, growing at about 3 per cent with a good deal of confidence if my recent visits there have been anything to go by.

Given WPP’s strengths there, its strategy of growing organically in growth territories or disciplines (and thus not burdening itself with unsustainable debt) plus some canny investments in digital and data, the group looks to be in good shape and is more than capable of hanging onto its place at the top of the hill.

But, as he often sagely does, Sorrell alluded to a black spot on the horizon, and it wasn’t in the Eurozone, or continuing uncertainty over the situation in Ukraine. It was in WPP’s home country. Outside of the USA, the UK is WPP’s single biggest territory, accounting for £221m of profit.

That black spot is May’s General Election. Sorrell warned the upcoming election contained risks to economic growth, whichever party wins the poll. He described the choice facing voters as a "Morton's Fork" – a piece of reasoning (said to have originated from John Morton, the Archbishop of Canterbury and Lord Chancellor under Henry VII) in which contradictory arguments lead to the same unpleasant conclusion.

"It's a difficult choice either way. If you vote Conservative, you are faced with a referendum over the EU either in 2016 or 2017. If you vote Labour, Labour seem to have a platform of criticising or bashing business so you worry on that count too," he said.

Sorrell – whom it’s reasonable to assume is a “small ‘c’” conservative – obviously feels, like most other businessmen, that the UK is best served by staying within the EU.

On the subject of EU membership, Sorrell said: "The issue is whether you can get any change [in Europe] before 2016 or 2017. I think the Prime Minister has drawn the potential date for a referendum forward to 2016, which would be better news. Less uncertainty as a result.

"But the key issue is our position in Europe – that's where the patterns of trade [are] whether we like it or not. They are not with the Brazils and Russias and Indias and Chinas. They are more with Germany and France and Italy and Spain.

"But reform it from within, best to be in inside the tent rather than outside the tent."

Advertising is a business affected by client and consumer confidence – perhaps more than any other industry. Uncertainty adversely affects confidence and willingness to spend.

I can see why Sorrell might be worried, but the truth is, after the polls close on 7 May, not much will change, at least in the short term. The smaller parties will probably do well, and the eventual winners – Labour or Tory – will have to think about making alliances.

But capitalism – of which advertising is an engine – will carry on as before, and if wages continue to rise faster than prices, confidence will keep on rising. And if it comes to the crunch a few years down the line and we have a referendum on EU membership, I think the public will vote to stay in; just as the Scots last year voted – albeit narrowly – to stay within the Union.

Why? Because when things are looking up – as they most undoubtedly are, in the context of the 2008 crash – nobody (especially those with families and mortgages) likes to rock the boat too much. Europe may infuriate many, and immigration from other EU members is a hot issue but, faced with the choice, most people would rather stay within the tent and grumble about it, than risk the uncertainty of what lies outside.

WPP still looks in better shape than any of its rivals – its like-for-like sales were better than either Omnicom’s or Publicis (Omnicom’s were up 5.7 per cent and Publicis’ 2 per cent), it topped the new business tables in 2014 and, despite Publicis’ recent purchase of the Sapient network, it still has a slight lead in digital. WPP’s sales are also $3bn more than Omnicom’s, and more than twice those of Publicis.

Given WPP shares rose 1.2 per cent on Monday after the results were announced, I’m not sure that Sir Martin has too much to worry about just yet…

Tony Walford is a partner at Green Square, corporate finance advisors to the media and marketing sector