I've had a chesty cough for over a week now I do smoke however this has never happened before any advice please?

Possibilities... Possibilities include bronchospasm from any etiology, gerd, sinus problems or a combination of factors. Since you are a smoker, you may have bronchospasm from copd. It is imperative that you quit smoking since this is an incurable and slowly progressive disease that will progress faster with continued smoking. See your doctor for evaluation and treatment.
Stop smoking. Give it a week or so if you don't feel ill, don't have a fever, or trouble breathing. You probably don't have cancer--yet--but a cought thant hangs on for weeks needs to be checked by a doctor. Keep smoking and you'll probably cough all the time anyway...