LONDON (AP) — A former British politician has been found guilty of murdering his wife after she found out he had an affair with their son's partner, the mother of one of his grandchildren.

Stephen Searle, an ex-soldier and a former local politician with the euroskeptic U.K. Independence Party, claimed he had been defending himself after his wife, 62, attacked him with a knife. But jurors agreed Tuesday the 64-year-old was guilty of murder.

Prosecutor Andrew Jackson said the couple's 45-year marriage had been under strain since Searle's wife discovered her husband's affair. He said Searle had probably put her in a choke hold, which he knew about from his military training, after "yet another" argument.

In an emergency call in December, Searle told police "I've just killed my wife."

Searle will be sentenced Wednesday.