Just because it's called a chile, that doesn't make it hot. I used to live in Colorado, and in the western US we had all sorts of peppers available - Anaheim, poblano, Fresno, jalapeno, habenero with greatly varying degrees of spiciness. In season we get both fresh and dried chiles from New Mexico and southern Colorado (Hatch's chiles are famous) which are flavorful, but not that spicy. Here in the Bahamas we have locally grown finger and Scotch Bonnet peppers which will singe your hair follicles. I can put 1/3 of a Scotch bonnet (that's about as big as the tip of my index finger to the base of the fingernail) minced in a pot of chili and it's as spicy as I can stand, and I like it pretty spicy.
I don't know what you consider spicy, and it's a very subjective taste. What I consider just pleasantly spicy would be much too hot for my wife's sister, yet I have friends who would consider it quite bland. If you want some control over the spiciness, you might consider ground cayenne pepper or red pepper flakes if either is available in the UK. Both tend to be more consistent and measurable than chilis.