(1) The Principal Act is amended -
(a) in section 2(1), by the substitution of the following for the definition of "year of assessment":
"'year of assessment' means -
(a) in relation to a period prior to 6 April 2001, a year beginning on 6 April in one year and ending on 5 April in the next year,
(b) the period beginning on 6 April 2001 and ending on 31 December 2001, which period is referred to as the 'year of assessment 2001', and
(c) thereafter, a calendar year and, accordingly, the 'year of assessment 2002' means the year beginning on 1 January 2002 and any corresponding expression in which a subsequent year of assessment is similarly mentioned means the year beginning on 1 January in that year;",
(b) in section 5(1), by the substitution of the following for the definition of "year of assessment":
"'year of assessment' means -
(a) in relation to a period prior to 6 April 2001, a year beginning on 6 April in one year and ending on 5 April in the next year,
(b) the period beginning o
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