He said his father had recently visited the races at Epsom, in Surrey.
"We are grateful to the honesty of the undertakers who returned the £2,000 found in his suit pocket," he said.
It was said of his father that he went out of his way "to find fools not to suffer", he added.
Sir Clement's wife, Lady Freud, read If I Should Die by Joyce Grenfell.
She said she had gone to a lot of trouble arranging a party for his 85th birthday.
"He would be amazed at how many of you have turned up and you are all welcome," she added.
The choir sang Oh, What a Beautiful Mornin', from musical Oklahoma - one of his song choices from his appearance on Radio 4's Desert Island Discs in 1967 - and I've Got The Horse Right Here, from Guys and Dolls.
The congregation sang hymns including Amazing Grace and I Vow To Thee My Country.
U2 frontman Bono and wife Ali Hewson were among guests
Other guests included Richard Curtis, Lord Steel, Paul Merton and David Morrisey.
The young Clement Freud began his career in the hotel business before he began writing about food for newspapers and magazines in the 1950s.
He later diversified into a number of different subjects, including sport.
Fronting pet food commercials with Henry the dog, first broadcast in the 1960s, launched his career as a TV and radio personality.
His political career began in 1973, when he won the Isle of Ely constituency for the Liberal Party, before he transferred to the North East Cambridgeshire.
Sir Clement, who was knighted in 1987, worked for a string of national newspapers.
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