Video: David Cameron attacks Labour's 50p tax rate plan as 'anti-growth' The Prime Minister defended his own decision to cut the top rate to 45p, insisting that while it may not have been popular, it was economically the right thing to do. But he dodged questions about whether he agreed with Conservative mayor of London Boris Johnson that the rate should be reduced further to 40p. But Mr Cameron told a conference of the Federation of Small Businesses in London that the Labour proposals may be "politically convenient" but would be "very, very bad for our economy."