To be honest, I don't find Lemsip does anything at all. No more effective than paracetamol on it's own. I think a bowl of hot water with a few drops of menthol & eucalyptus & cover your head with a towel & breathe in the steam. Also if you are taking anything for blood pressure you might need to check with your GP, mine told me to only take decongestants like Sudafed if I wanted some relief when going out for the evening say.
PS I've mentioned it on another post but rubbing some Vick into the bottom of your feet before bed & covering up with socks gives some relief. Don't know how it works but it does