Brexit has already damaged the UK’s “global brand”, according to the head of the world’s largest advertising conglomerate.

Writing exclusively for The Independent, Sir Martin Sorrell, the chief executive of WPP, suggests the xenophobic tone of the 2016 referendum campaign did serious harm that needs to be repaired and that Theresa May’s Brussels deal on 8 December over European Union citizens’ rights was merely the necessary first step.

“It doesn’t ... address how we will continue to attract the best and brightest from across mainland Europe and beyond after Brexit, or repair the damage already done to the UK’s brand by the divisive rhetoric during and after the referendum campaign,” he said.

During the run-up to the referendum, the official Vote Leave campaign pushed hard on the benefits of curbing immigration and notoriously claimed that Turkey was about to join the European Union.

Police figures also showed a clear spike in hate crimes in the wake of the vote.

And the latest migration official statistics showed a sharp increase in the number of EU citizens leaving the UK in the year to June 2017.

Sir Martin Sorrell (Reuters)

Sir Martin said that WPP, which he established in 1985 and is now worth around £17bn thanks to decades of acquisitions, has a particular interest in the wellbeing of EU citizens in the UK since they account for around 15 per cent of the company's 17,000-strong British-based workforce.

In some divisions the proportion is pushing 30 per cent.

Sir Martin, who supported Remain in the referendum, also says that, despite this month’s Brussels deal, there is a “long way to go” to end the uncertainty for UK firms about future trade relations with Europe.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

“Uncertainty will be a fact of business life for at least as long as it takes to negotiate a new trading relationship with the EU, if there is one,” he said.

“Until that happens, many companies will continue to delay or cancel decisions to invest in the UK.”