Socially useless banks?

From the Guardian newspaper... Lord Turner (top financial regulator in the UK) wants to tax "excessive profiteering" by "socially useless banks" in the UK.

All this sounds like a slippery slope to me. What is "excessive" and does he really think that banks are "socially useless"? He also talks about "simplistic regulation". I don't think it was lack of regulation that lead to the particularly bad financial mess in the UK, just bad regulation. In particular, the government took the implicit role of lender of last resort to banks that are too big to fail. Instead, the government should regulate capital standards that are a function of the bank size.

Elsewhere in the article Turner questions whether the financial sector has grown too large. In a free market, capital will move to the the most productive use. In the UK, this turns out to be the financial sector, in part because there isn't much in the way of a significant manufacturing sector anymore. The only way that I could conceive that the financial sector was "too large" is if it is receiving some sort of government subsidy, such as an implicit guarantee. In which case, we know who to blame.