That is a very good point, which leads me to the two quotations that I was about to give. Paul Johnson, the head of the IFS, said in a paper that was published on 27 January 2014:
“The best available estimate of what reversing the cut would raise is therefore about £100 million too.”
He also said that
“the best evidence we have still suggests that raising the top rate of tax would raise little revenue and make, at best, a marginal contribution to reducing the budget deficit an incoming government would face after the next election.”