From Chris Dillow:
A wage ceiling allows lackeys of the rich to whine that Labour hates the well-off. We should reframe the policy. Rather than say nobody should earn (say) 20 times more than the lowest earner we should say that nobody should earn less than one-twentieth of the top earner. We should call the wage cap a wage floor.Obviously one can argue about the ratio. And there may be cases where this sort of blunt policy would be problematic. But as a cap, it is much better to frame it as raising low incomes than capping high incomes.
If the ratio wasn't a cap, but a test for a "3% excess earnings tax" (or something else) then the top level makes more sense. A modest tax on high ratio earnings would raise revenue but would be unlikely to create inefficiencies as saving a few percent isn't going to make dramatic tax avoidance strategies all that effective. Then the framing rather needs to be on the cap and not the floor, although it would create a management pay-out for making sure the lowest paid workers aren't under-paid.