More than 350 banks in the EU have increased in size during the past two years, including Barclays, BNP Paribas and Santander.
Fifteen European banks now have more assets than the economy of the country they are based in, reports Bloomberg.
David Lascelles, a senior fellow at the UK-based Centre for the Study of Financial Innovation, said it appeared European banks had not learnt the lessons of the economic crash.
"We are sowing the seeds for the next crisis," he stated.
"It really goes against the currents of the time."
The Royal Bank of Scotland (RBS) increased its assets by almost 3,000 per cent in the ten years up to 2008.
When the financial crisis occurred, the British government deemed it too important to fail and bailed it out to the tune of $76 billion.
RBS posted an operating loss of $2.5 billion in its last quarter.
By Asim Shah