People looking for anything between a quiet laugh and a fit could try the books of Peter Tinniswood:

eg Winston
     The Brigadier series
     Uncle Mort's South Country

But one of the funniest books I ever read (I could have mentioned it before) was The Matchmaker of Perigord by Julia Stuart.
It was her first book and I was so bowled over by it that I wrote to her through the publishers.
This is the email I got in response:

Dear Mr ****,
"I have just received your lovely letter which was forwarded to me by my British publishers. Thank you for taking the time to send me your kind and generous comments. Those Limousin cows do really wink as you walk past them! I haven't in fact read any books by Gabriel Chevallier (1) or Giovanni Guareschi (2) but I will order some out of interest. I am currently reading Three Men in a Boat by Jerome K Jerome which is the funniest thing I've read in a long time."

(1) the Clochemerle series & (2) the Don Camillo series, also humorous books which I had mentioned to her as reminiscent of her own humour.