The only thing to be aware of is coming off megadoses slowly, even once the illness has headed for the hills. Continue to take the C for a couple of additional days while progressively lowering the dosage.
And those on birth control pills remember it can affect them too, particularly when you stop taking the vitamin C. Can't remember why though, just remember learning about it in Biochem class.
Also anyone with a common cold shouldn't be taking antibiotics or really even going to the doctor (if it's doctor-bad it's not likely to just be a cold). Rest and fluids really are the best cure (this one I can even remember the biological reasons why too :)).
2 painkillers 2 lemsip extra strength
You probably want to only do one of these, assuming Lemsip is the same as it is here (vitamin C and paracetamol/acetaminophen). Otherwise you'll be doubling up on the painkillers which isn't very good for you and doesn't really increase the painkilling affect.
And you want to make sure that honey is manuka for maximum effect :)