Hi our bedroom floor which is concrete, is condensating under the carpet, and is noticeably wet, along with the outside corners of the room being damp with black mould, can anyone tell.: me what they think is the problem

You have water leaking into the floor somewhere along the foundation outside. Best to address this problem before the mold sitaution gets worse. You need to seal outside the room as soon as possible. Take the carpeting out of the room and dispose of it as it already has mold spores in it and will just be a breeding ground for more mold compounding the problem. Mold is not easy to get rid of. I've heard of a new product that can be used with a large pump sprayer. Don't know the name of it but it is sold I believe at Lowe's. It should be used after you properly fix the leak and after you thoroughly dry the area. Use the spray and then properly air out the room.

I agree, this does not sound like condensation at all. The carpet is a goner so take it up and find the leak/seepage before you disinfect the floor and recarpet.