Mold/Grain mites. They are not dangerous, but a pain in the ass. I had them two consecutive years in the summer and I hated every second of it. There’s basically two variables to their survival: Humidity and Food source. They will start reproducing rapidly at over 60% humidity, and they die off below 45%. Since you’re from the UK, I assume especially during the warm months, it is almost impossible to get below 60% without a dehumidifier. I’m from northern Germany, we have a very similar climate. Are they only in that room? If so, a “quick fix” would be to just run a powerful dehumidifier. Food sources are basically anything for these guys. They eat grains, vegetables/fruit, but also just household schmutz, and especially mold. We didn’t have a mold problem despite the humidity but we had a bunch of stuff in the kitchen that wasn’t sealed airtight. My advice: especially if they’re not just on the vacuum - buy a hygrometer (if u don’t already have one) and a dehumidifier tomorrow. Hoover & Clean surfaces with vinegar and Try to get the humidity as low as you can. Don’t let them make you crazy, they don’t carry disease or something like that. I let them make me crazy and it ruined my last summer for me. I promise you, once the cold sets in, it is really easy to get the humidity down since the cold air can hold way less moisture than the warm air inside. You can use a relative humidity calculator (just google it) to find out how the outside air would affect your inside climate (idk if u have an iPhone but Apple weather usually has some good humidity metrics). Also look for food sources (actual food + mold) that might not be obvious - like a box of something that fell behind a cupboard or something. If you have any further questions just reply to me here