5(1)If the Board discover that any company which—
(a)has made a return in relation to which paragraph 4(4) above applied, or
(b)has been assessed to an amount of windfall tax,
has not been assessed to as much windfall tax as it should have been, they may make an assessment or further assessment of the amount which, in their opinion, is windfall tax with which that company is charged but to which it has not been assessed.
(2)Where—
(a)the Board discover that an amount of windfall tax has been repaid which ought not to have been repaid, and
(b)that amount is not assessable under sub-paragraph (1) above,
that amount may be assessed by the Board, and recovered under this Schedule from the company to which it was repaid, as if it were an amount of windfall tax which that company is liable to pay.
(3)Where the amount of any assessment to windfall tax is reduced, the company assessed shall not for the purposes of this paragraph be treated, at any time after the reduction, as having been already assessed to the amount of windfall tax comprised in the reduction.