US President Barack Obama (L), seen here with British Prime Minister David Cameron at the Nuclear Security Summit in Washington earlier this month, is set to back Britain's continued EU membership on his visit to London
London (AFP) - Would leaving the EU make Britain "great" again or risk its global power status?
US President Barack Obama is set to back continued membership on a visit to London Friday but "Leave" campaigners say the world's most powerful man is wrong.
Over 100 anti-EU MPs signed a letter urging the US president not to intervene in the debate over the June referendum ahead of his visit to London. The White House has already said it wants Britain to stay.
The visit by the popular leader of Britain's leading international ally has helped crystallise arguments on both sides about whether it would be stronger in the European Union or outside it.
The "Leave" camp are fighting to convince voters that, free of EU red tape, Britain's best days could be ahead of it, not behind it following the mid-20th century decline of the country's empire.
Pro-Brexit figures list a string of nations which Britain could emulate.
London Mayor Boris Johnson points to Canada, saying Britain could strike a series of free trade deals and cut tariffs. Others look to Norway or Switzerland.
"If we hold our nerve and we're not timid and we're not cowed by the gloomadon poppers (pessimists) on the 'Remain' campaign and if we vote for freedom and the restoration of democracy... then I believe this country will continue to grow and prosper and thrive as never before," Johnson told a campaign event last week.
In response, Cameron warned that voting "Leave" was essentially a "leap in the dark".
- 'Unwanted headache' -
The stakes are high -- not just for Britain, but globally.
Britain has the world's fifth-largest economy and defence budget. It is a member of NATO and has a permanent seat on the UN Security Council.
The country has close ties with both the US and China, with ambitions of becoming the "best partner in the West" of Beijing.
The "Remain" camp argues that Britain is stronger inside the EU, from where it can help negotiate collective trade deals and foreign policy decisions.
Tim Oliver of the London School of Economics, a specialist in British foreign policy, said Brexit would cause the US an "unwanted headache".
"The UK has a special relationship with the USA but that is most true in the three areas of nuclear weapons, intelligence and special forces," he told AFP.
"The wider relationship fits into a much wider and special US-European relationship."
Oliver argued that a Brexit would also cause problems for Beijing, adding: "Few in the UK appreciate that one of the longest-standing supporters of European integration has been China."
As for the free trade deals which Johnson and others suggest Britain could cut from outside the EU, some academics are sceptical.
Paul James Cardwell, an EU law expert at Sheffield University, argued that such post-Brexit agreements would depend on the state of Britain's relationship with the EU at that point -- including whether it could access the single market.
"The choice seems to be remaining in the EU with current agreements... or leaving in the hope that states respond positively to the UK," he said.
"There is no evidence yet to suggest they would do so, and plenty of evidence to the contrary."
- History of euroscepticism -
Those who want to leave the EU warn that there are major risks associated with continued membership.
"If you're in a structurally unsafe building, the obvious alternative to remaining is walking out," eurosceptic Conservative MEP Daniel Hannan wrote in the Daily Mail this month.
"With the migration and euro crises deepening, the EU is just that -- structurally unsafe."
History also plays its part in the argument for Britain leaving.
Many do not see themselves as European. A European Commission survey last year found that 56 percent of Britons saw themselves as citizens of the EU, compared to a 67 percent average in the rest of the bloc.
Britain is separated from mainland Europe by 20 miles (32 kilometres) of sea and centuries of battling the Romans, French and Germans.
When its colonial power withered following World War II, Britain tried to get into Europe, only to be vetoed twice by France. It finally joined in 1973.
Since then, its mainly eurosceptic press has delighted in ridiculing Brussels while a string of leaders like Margaret Thatcher have had frosty ties with the EU.
Anti-EU Britons may protest about people from overseas telling them what to do -- but Cameron will be hoping that, in Obama's case, a foreign intervention can help save the day this time.