That wikipedia article seems to have disappeared, so instead, taken from the book "POMPEY - The History of Portsmouth Football Club" by Mike Neasom, Mick Cooper & Doug Robinson:
Some claim it lies in an 80-gun French warship Le Pompee captured in 1793 which later fought with distinction in the battle of Algeciras in 1801 and then became guardship of Portsmouth Harbour. Others maintain it was the product of a far from sober sailor's interruption of a talk by AgnesWeston, the naval temperance worker. He surfaced from a beery slumber during her lecture on the Roman Empire to hear that the general Pompey had been killed. 'Poor old Pompey' he is said to have shouted . . . . such are the roots of legend. Bu there is another more authenticated potential root in Naval folk-lore. In 1781 some Portsmouth-based English sailors scaled Pompey's Pillar near Alexandria and 98 feet up above Egypt, toasted their ascent in punch. Their feat earned them the Fleet's tribute as 'The Pompey Boys'.