Ballooning central bank balance sheets across the U.S., Europe, the U.K. and Japan are "profoundly abnormal", according to Jean-Claude Trichet, the former president of the European Central Bank.
"If you look at the increase in the size of balance sheets since the crisis erupted in 2007, you see the same order of magnitude: at least 12 percent of gross domestic product… You see something which is profoundly abnormal in the U.K., Japan, Europe, and the U.S.," Trichet told CNBC on Friday.
According to its own data, the Bank of England's balance sheet topped 20 percent of annual gross domestic product (GDP) in the first quarter of 2012, and was roughly four times larger than at the start of 2007.
In the same period, the Federal Reserve's balance sheet reached more than three times its pre-crisis size and neared 20 percent of GDP, while the European Central Bank (ECB)'s balance sheet topped 30 percent of euro zone GDP.
"I expect we will not remain eternally in the present situation. This situation is not the new normal that is acceptable," said Trichet.
"It takes time and effort and also a lot of strong messages coming from the constituencies of central banks."
Much of the expansion of the Federal Reserve and Bank of England balance sheets has been driven by their purchases of government bonds.
(Read More: Quantitative Easing Explained)
Meanwhile the ECB's balance sheet has been inflated by its long term refinancing operations (LTROs) to banks.
(Read More: LTRO Explained)
UK Exit Won't Hurt EU
Trichet also told CNBC that the European Union would be unharmed if the U.K. chose to exit.
"It is a problem for the U.K.; it is not necessarily a problem for the Euro," he said.
"Let us not forget that even without the U.K., the population of the euro area is already more numerous than the U.S… On top of that, you have a number of countries that are eager to enter. In particular, the biggest is , which is the biggest country in central and eastern Europe."
(View More: The Cost of EU Membership for Croatia)
Pressure has been mounting on U.K. Prime Minister David Cameron to hold a public referendum on E.U. membership. Eighty-one members of his own party voted in favour of a referendum in November last year. Cameron has also appeared to be distancing himself and the U.K. from the rest of the European Union during recent budget, bank supervision and policing discussions.
(Read More: Brixit Looming? UK Looks Sidelined With Veto Threats)
Trichet was critical of the referendum calls however.
"I thought a referendum was a Napoleonic concept not fitting with representative democracy the U.K. invented," he said. "My own experience is that the U.K. does not lose sight of her own interests, and puts her own interests first."
Others have also argued that a British exit from the European Union – or a "Brixit" as it has become known – would not benefit the country.
There might be in some people's minds some benefit in the short-term, but in the long-term I'm not sure it's positive," Societe Generale CEO Frederic Oudea told CNBC on Wednesday. "So I hope the U.K. will resist this temptation."
"Of course if you belong to a group, club or team you need to agree and comply with the rules; that is the trade-off," he added.
- By CNBC's Katy Barnato