Of Kerrison’s father an obituary had this to say:
Born in an inferior station of life, and enjoying few of the advantages of education, Mr Kerrison had accumulated by trade, and good management, property of little less value than a million sterling, which is much of it invested in the fine estates of Lord Maynard and the Marq[uess] of Cornwallis. His own habits of life were of a very plain kind.
Gent. Mag. (1827), i. 477.
Kerrison entered the army, serving in the Helder campaign in 1799. He proceeded to the Peninsula and was severely wounded at Leon in December 1808, but distinguished himself in the later stages of the war and at Waterloo.
In 1812 he stood for Shaftesbury on the interest of its new patron Robert Peter Dyneley.
He was successful in a contest at Northampton, where he found a fortuitous opening, in 1818, but inactive in the ensuing Parliament, taking leave of absence for ten days in March 1819 and pairing in favour of the excise duties bill, 18 June. He was out of the next Parliament until he purchased the borough of Eye.
