You would think that a tax advantage that applies to everybody cannot give anyone an advantage. The GMB trade union, however, does not see it that way. It argues that taxing profits after interest has been deducted gives private equity an unfair edge. But while the GMB has spotted a real issue - the tax system discriminates between debt and equity - private equity is hardly to blame.

The GMB is angry about job losses at some private equity-backed companies and its complaints have been echoed by some candidates for the deputy leadership of the Labour party. The GMB's argument is that because one private equity strategy is to load the businesses it owns with debt, which reduces taxable profit, buy-out firms have an unfair advantage.