I have been told that after soaking the red kidney beans you must boil them for at least ten minutes before further simmering, to destroy the poison.

Does anyone know at what stage runner beans from the garden might become poisonous? Would it only happen if they are dried and then soaked, or are they a different variety of kidney beans?

Didn't see an answer to this (apologies if someone has & I missed it), Jos. The 'poison' in red kidney beans is something called phytohemagglutinin (AKA 'muck'!). Boil for 15 minutes after soaking; for 30 minutes if unsoaked is the usual advice.

It seems that ALL beans contain this compound to some degree. It's only bona-fide toxic in high doses, but I can speak from personal experience here. I can't remember now whether the salad I made included home-grown broad beans or green (French) beans. I do remember I had to cry off my game of squash after work. Two to three hours after eating it, I threw up the entire bloody lot! Red Kidney beans have a higher concentration of Muck, but all beans contain some of it, so never eat 'em raw! No, the concentration won't increase once harvested, whatever the bean. But equally, always cook the raw bean!*

*Canned beans were cooked before canning...