The Patriotic Nurse has a video on this, she recommended a company but we found out they no longer ship to the UK and to get them here I think you need a prescription.
This mainly works for smokers but try it any way, breath deeply and slowly in and out through your nose, count the breaths same in and out,increase it to your lung capacity, even most non smokers don't breath right and will have some crap in their lungs, do the test, place your hand over your stomach take a breath in, does your tummy go in or out on that in breath? it should go out.
after a while of this even the best of lungs should be able to clear some crap from the base and cough it up, the trick is not to cough it up but hold it half way, to a Doctors ear that's a chest infection and you'll get antibiotics ,I get one about every 3/4 months