How to use overgrown beans

Thsy are not Runner beans they are Kidney beans and have a natural toxin in them which need boiling before they are safe to eat. You need to research how much boiling they need to make them safe.

I've taken out the beans from runner beans (also French beans) and used them without even thinking they might be toxic. I'm pretty sure red kidney beans are different.

I was wrong in post above- runner beans do have small amounts of a toxin but it's destroyed by cooking.

www.theguardian.com/lifeandstyle/2010/aug/28/alys-fowler-runner-beans?CMP=Share_AndroidApp_Other

In the past, I have let various types of bean, including runner beans, mature and dry in the pod, then stored them in airtight containers, using as required over winter.

I simply treated them all as i would dried kidney beans so yes, I did boil them first for a certain length of time, though having not done this for a while I cant remember how long.
No need to use the freezer that way, although I also stored some mature but not dried beans that way.

I used to make a kind of 'felafel' out of many of them.

I think they are exactly like kidney beans for toxins if dried.

This is a traditional method...
Soak till fully plump (or overnight).
Throw the water away.
Bring to a hard boil for at least 10 mins.
Cook till tender.

Yes. They have the same toxins.
Phytohaemagglutinin (a toxic lectin). Eating raw or undercooked runner beans can cause severe nausea, vomiting, and stomach cramps.

If in a hurry I put them in cold water, bring to the boil and boil for at least ten minutes then throw the water away and do this again before cooking till soft.
If the beans are really old/hard they won't cook evenly though and those will need to be soaked or the core will still contain toxins and the outside will be mushy before the middle is cooked.

According to the sites I looked at different beans contain different levels of lectin. Red kidney beans have the highest levels but most other beans have low to moderate levels.

The symptoms of lectin poisoning seem to be similar to food poisoning, nausea, vomiting and diarrhoea, but it is not fatal excepting in vulnerable people eating high concentrations.

As far as I can see, eating properly cooked mature runner beans are not a problem.

Exactly.
Properly cooked is the key.

We have been cooking all sorts of dried beans beans for my whole lifetime with no ill effects.

They're probably safer than my mother's cooking or my husband's & certainly my son's ..we call him disaster chef!