I've known Alastair Darling's style on Treasury issues for a long time - since before Labour came to power in 1997. So I'm not surprised that he has (according to the FT):

ruled out an immediate clampdown on tax privileges used by the private equity industry, fearing that any sudden changes might have undesirable effects on the "absolutely critical" role the City plays in the economy.

and that he added that: he would:

always strive in making changes to try and make the [tax] system simpler, but would not make quick changes to capital gains tax or the taxation of individuals not domiciled in the UK, even if it would gain favourable headlines.

The only trouble with this is that he has his decision process wrong. This has nothing to do with favourable headlines. Tax rises rarely achieve that goal. This process has to do with justice, economic efficiency and supporting the effectiveness of the the markets within the City. I'm worried that he has not cited these reasons for action, because as it is the tax rules create market abuse, and that's the core of the problem.