This is a recipe for pickled chillies that I made today, based partly on what my father-in-law Grandpa Josh used to make, and partly on all the recipes that I see on the webs, for example this one.
I put a 900ml jar and lid in the oven at 100C to sterilise.
I put in the jar 160g green chillies, lots of peeled garlic cloves, one yellow and one red pepper. In a pan I boiled approx 300ml cider vinegar (because a friend gave me 5 litres of it that they made accidentally when trying to make cider) to which I added a dessert spoon of Muscovado sugar. I poured the vinegar into the jar, topped it up with boiling water, and immediately put the lid on.
Edible from the next day, will keep for a few weeks. The chillies are quite a bit less hot than they would be raw, but the peppers gain quite a bit of heat.