I take from your location, Salisbury, UK (great place by the way) that your enlarger is not sitting in the basement, correct? If so, have you ever measured the humidity level of the room the enlarger is in. It still being relatively cold, your air might be too dry, and you have more than normal static and, consequently, dust. See if this problem gets less during the summer months. If yes, a humidifier may help. Some darkroom workers spread out a wet towel a few hours or so before they print to get the humidity up, but I have not tried that. I don't print without glass carrier anymore. I find it almost impossible to get a really sharp print without them. I rather dust than compromise on sharpness.