I wanted to add in that taking a good MultiVit is essential when stopping. I am recomending
"Berocca ". Information is available from there website at berocca.co.uk/
I bought mine from Tesco because they had an offer on and i suggest that everyone take something like this each morning to help rebuild your immune system. These particular ones are high strength and can help with concentration, sleep, energy etc etc.
I have found them brilliant and even though they are slightly expensive we are all saving money now from not smoking so its worth paying out to get decent vitamins.