Fungus Gnats or more sinister?

Just wanna say thanks for the replies, I shall give your suggestions a whirl and see how I go! Thanks chaps 👊🏼

Hard to say what it "could be" without any details or pictures. But diatomaceous earth on top of soil, will take care of most larvae and non flying bugs.. Even flying ones, as they land to lay eggs in the soil. - If you figure out what type of bug it is, you can order predator mites online,, and have them take care of anything crawling on the plants.. You'll have to know what type of insect it is tho, as there's a wide variety of predators, where most specialize in a few types of insect and might not eat other types at all. Imagine yourself as a general giving orders to your own little army of bugs. Like a real army, you'll want something effective against the opposition, a tiny machinegun won't destroy a tank, and a tank is pretty useless against people running around in tunnels under it. - Also, you'll love the Diatomaceous earth.. Imagine getting a million tiny cuts on your body, draining you of any fluid. It's a painful death. That's what DE does to insects, and 100% worth the money.

I agree with the @8thChenvron, also you can set some yellow sticky traps to kill the flying adults and also put a layer of diatomaceous earth on the top of the pots as this cuts them to pieces on impact when the young try and leave the soil. A Fungus gnat killing product I recommend is Neem oil when you follow the directions and use a pressure sprayer/mister so it gets distributed which is a option over the diatomaceous earth which should kill the young in the soil. A fan to blow air over the top of your soil to keep it from being too wet which is what they like and also to stop the adults landing in the soil and laying larvae. All the above stuff you can get in Growell which have many shops around the UK. That covers everything I think and hope this helps👍 Happy growing pal

For fungus gnats the best thing you can do is eliminate their breeding grounds. If in soil, make sure that the topsoil is dry for at least an inch deep before watering. For coco, just make sure it's not always soaked. You don't want the top to completely dry, but you don't want it to be dark colored and super wet all the time either. This tends to correct the problem without any traps or pesticides requred.