I've looked at the other thread and this and I'm a bit confused. On what grounds are you giving notice?
When does his contract end? Because the 1 months notice on a years lease is in regard to ending the lease at the 12 month point AFAIK. I'm fairly sure you have to give 2 full months notice to quit otherwise.
If you are giving notice because of late rent, he has to be at least 2 whole months behind with his rent.
I'm not sure where you stand on evicitng him on grounds of the neighbours complaining.
The fact that you have continued to let to him knowing he smokes/pays late etc will make the court likely to side with him, so you need to know what you are doing.
Evicting a tenant is very difficult. You have to do exactly the right thing at the right time. If you make a small mistake you get sent back to square one and have to start again.
From personal bitter experience in a cut and dry case for me (no rent full stop and major damage to the house) it took over a year to eventually get rid of my tenant and cost me thousands of pounds. And that was just the legal side, never mind the damage she continued to cause to the house that was truely wrecked. Like had to strip it back to the jpoists wrecked.
I think you need to be very carefull WRT how you approach this, and you need to decide if you can put up with the situation untill the lease ends. It is a pain chasing rent but at least you are getting some.
I would take the issues of the other residents seperately. Again you will have to check out what your legal responsibilities are wrt this (I have no experience of flats).