The idea of the IWF was basically taken from the U.S. where the Republicans created a nominally independent but hardly independent "charity" to circumvent the law.
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It always made more sense in the U.S. though, because the U.S. actually has meaningful restrictions on the federal government.
That said though, maybe it still affords someone a measure of psychological security, when you consider what the Tory Government has been up to for the past few years.