Why did George Osborne sack FCA CEO Martin Wheatley?

Financial Conduct Authority (FCA) CEO Martin Wheatley was sacked by George Osborne despite, in Osborne’s own words, having “done a brilliant job of launching the FCA in tough circumstances”.

So the question is – was he sacked because he wasn’t being tough enough with Bankers and others in the City or because he was being too tough?