Former taoiseach John Bruton says the UK will suffer a major loss of influence on the global economy if it votes to leave the EU.
He said membership of the EU enhanced the ability of European countries to influence issues like globalisation, the rules governing international financial services and trade.
“Membership of the EU gives the UK a seat at the table when international trade agreements are being made,” he told an investment seminar that was hosted by Appian Asset Management.
“The EU helps set the rules for global services and goods trade, and if the UK opts to leave the EU, its voice will simply not be heard when it comes to setting those rules. Opting out of the EU would thus diminish UK sovereignty.”
Mr Bruton said the loss of influence could be catastrophic for UK businesses and consumers.
"That will be bad for Ireland because we do so much business with the UK. If the UK leaves the EU that will drive up the cost of living here because of the cost of applying tariffs and customs control to goods transiting through the UK," he added.
Separately, former British prime minister Gordon Brown has warned of the potentially damaging consequences for both Britain and Ireland of Brexit.
At an event hosted by PwC Ireland in Dublin, Mr Brown said: "People often forget that Ireland is the UK's biggest trading partner after the USA, France, Germany and the Netherlands.
"The UK and Ireland are so closely interconnected as members and partners in the European Union that a British exit from the European Union would hurt both.
“We share a common agenda to open up the European single market to digital, energy and financial and service sector firms thus creating thousands of jobs in our two economies. Without the UK, there might be a blocking minority to prevent the changes that are needed,” he said.
A new YouGov poll for the Times newspaper showed opponents of Britain's EU membership edging into the lead in the run-up to the June referendum on the issue, despite an intervention on the "In" side by US president Barack Obama.
The online survey, taken on Monday and Tuesday, showed support for the “Out” campaign had risen 3 percentage points to 42 per cent since a similar survey on April 12th-14th, while the number of undecided had fallen, leaving support for the “In” campaign up 1 percentage point at 41 per cent.
