The flat income tax

Your answers to questions 21 to 24 must be based on the
text below entitled "A dip in the middle":

A dip in the middle
Source: The Economist (adapted)
Sep 8th 2005

Income tax has been paid in Britain for more
than two centuries. First introduced by William Pitt the
Younger to finance the war against Napoleonic France,
it is the Treasury´s biggest source of revenue, raising
30% of tax receipts. It arouses strong political emotions,
regarded as fair by some because it makes the rich pay a
bigger share of their income than the poor, but unfair by
others because it penalizes enterprise and hard work.
During the past 30 years, income tax has been
subject to sweeping changes, notably the cut in the top
rate from 98% to 40% under Margaret Thatcher between
1979 and 1988. Now another Conservative politician,
George Osborne, is floating a radical reform to match
that earlier exploit. The shadow chancellor announced
on September 7th that he was setting up a commission
to explore the possible introduction of a flat income tax
in Britain.
Introducing a flat income tax into Britain would
involve two main changes. At present, there are three
marginal tax rates. These three rates would be replaced
by a single rate, which would be considerably lower than
the current top rate. At the same time there would be an
increase in the tax-free personal allowance, currently
worth 4,895 pounds.