Even the Red Book says the government will get more revenue from increasing the tax on jobs than the 50p rate.
The Red Book says that increasing the rate to 50p on income over £150,000 would raise £1,810 million in 2011-12. By contrast, raising employees’ national insurance contributions by 0.5 percent brings in £1,960 million in 2011-12 and the 0.5 percent rise in employers’ NICS would pull in £2,460 million. (In reality, the 50p rate will raise a lot less, as any proper dynamic model would tell you.)
The 50p tax rate is a diversionary tactic, a political measure designed to divert attention from the fiscal mess. The idea that it can seriously help address a national debt that will amount to 79 percent of GDP in 2013-14 is just a joke.