DAVOS, Switzerland - "Keep it simple, visual and factual" - that is the advice of the most powerful man in advertising to Britain's campaign to stay in the European Union, saying it must focus on the benefits to trade, investment and jobs to win the debate.
A second-generation immigrant, Martin Sorrell, who has built the world's biggest advertising group WPP (WPP.L) over 30 years, is passionate about staying in the EU and does not rule out personally contributing to the 'in' campaign at a later date.
But if Britain were to vote to leave the 28-nation bloc in a referendum Prime Minister David Cameron hopes to hold this year, he would feel a conflict between his head and heart - with logic suggesting that he should move his headquarters from its now home, while patriotism may compel him to do otherwise.
"Keep it simple, make it as uncomplicated as possible, make it as visual as you can possibly can," he said in an interview at the World Economic Forum in the Swiss resort of Davos.
To make his point, he cited a poster campaign carried out in 1979 by advertising company Saatchi & Saatchi, where he worked at the time, on behalf of Britain's then opposition Conservative party under Margaret Thatcher.
The poster, showing a long line of people queuing for unemployment benefit under the slogan "Labour isn't working", is credited with helping the Conservatives win that year's parliamentary election.
Sorrell did not suggest what the catchphrase for the 'in' campaign might be, saying: "That's not my job." But he urged it to offer an alternative vision of immigration as a positive force to counter a growing feeling among some voters that Britain is already a "crowded isle".
"As a second-generation immigrant, and I am probably subjective about it, I think immigrants are a net benefit not a net disadvantage," said Sorrell, whose father's parents were from Ukraine and mother's were from Poland and Romania – the first arriving in England around the turn of the 20th century.
The referendum will not only shape Britain's role in world trade and affairs, but also the EU, which is struggling to maintain unity over migration and financial crises.
Although official campaigning on both sides of the debate will not begin until Cameron has finished negotiations with the bloc which he hopes will secure a better membership deal for Britain, the battle lines have already been drawn.
Much of big business in Britain has sided with Cameron, pressing arguments that the EU's single market helps spur trade, attract investment and create jobs while the uncertainty of a possible 'Brexit' does little for the economy.
Some smaller businesses and hedge funds are keener on leaving the bloc. Others say an exit would have little impact.
Roger Carr, chairman of BAE Systems (BAES.L), Europe's biggest defence contractor, supports remaining in a reformed European Union and says there is an understanding that business should support the government's position to negotiate a better deal.
"I am a supporter of making it better, more competitive and therefore seeking to improve it, but I still believe you can do that more effectively as a family member within rather than as a critic outside," he told Reuters.
Although an exit would not directly hurt BAE, which mostly deals with governments, he said the tone of relationships would change and it could hurt security. He is not working on contingency planning if Britain votes to leave.
But Dominic Barton, global managing director at McKinsey business management consultancy, said some other companies were spending "a lot of money" on planning for a British departure which could mean moving offices out of Britain.
"I know one global bank that is spending $75 million, because you've got to think about (your) real estate footprint, moving people, tax implications," he said.
"And even though you don't think it's going to happen, as a leader you've got to have a backup plan."
EMOTION OR LOGIC
For Sorrell, his team as yet have not started looking into a move, which, he suggests, would be a wrench.
He moved WPP, which owns agencies including JWT, Ogilvy & Mather and Grey, to Ireland in 2008 to cut its tax bill after the then Labour government proposed the potential "double taxation" of corporate profits. He returned in 2013, but said some board members were against it.
He said the company returned for "I hesitate to say it" patriotic reasons and some board members were against it, making it "difficult to say" whether the company would move again.
"And forgetting about the emotional side for a minute ... purely logically ... if we came out of Europe it would probably make sense to be in Europe. It could be Paris, Berlin, Madrid, Milan, Frankfurt," he said, adding there was no plan to do so.
Most business leaders are, like many opinion polls, split over which side of the debate has the upper hand. Some polls suggest that those favouring a departure from the EU have a small lead but with so many Britons undecided, any clear picture is difficult to gauge.
That's where a simple campaign comes in, says Sorrell, who argues that many of those as yet undecided over which way to vote simply do not have enough information.
"If I look at the polls ... (they are) saying the key battle ground is the undecideds," he said.
"And the key battleground with the undecideds apparently is that they say they haven't got the information. So it would be about laying out the case cogently ... It's very easy, you take the leading factors and you just lay them out - investment, trade and jobs."
(additional reporting by Martinne Geller; editing by Anna Willard)