Have found a William Whitton in a book about Tandragee:
born c1804 Tandragee, labourer by trade
5'7" in height, fair hair, grey eyes and fair complexion
Enlisted in Newry 06/06/1822 aged 17
10th Regiment of Foot
discharged 19/06/1843 aged 39
Service included 15 months in Portugal (from 01/01/1827) and 10 years on the Ionian islands.
Karen