US-OWNED CEREALS GIANT Kellogg Company of Great Britain, currently celebrating the centenary of the ubiquitous cornflake, is marking the occasion with its largest-ever UK promotion - the 100th Birthday Bonanza competition, top prize for which is £100,000-a-year for life, with each instalment payable on the winner's birthday. However, there is a fly in the ointment [or, rather, the cornflakes] in the shape of the equally ubiquitous taxman. Following lengthy discussions between Kellogg and the Inland Revenue, Hector will get his share of the windfall. Although promotion prizes are normally tax-exempt, this differs because Kellogg is financing the prize via an annuity in the winner's name. [Hector never misses a trick!] No-one is sure how much tax the winner will pay as Kellogg's has yet to confirm how much of the annuity is taxable; the amount will also depend on the winner's marginal tax rate.