I have read that some people have fans installed which help with poor chimney draw - on a downside these can make a slight bit of noise.
Also lining the chimney should help (I think) as the flue/chimney will heat up quicker & I think a warm chimney will disperse smoke quicker. Some have mentioned that getting the chimney lined can total around £1000
I did find this info which someone had posted on a forum.
Assuming that the chimney is being used for a standard fireplace, I'd recommend buying a "certified" fireplace insert. They use smaller chimney pipes (mine uses6") to work properly. You'll get big bonuses on heat to the house. Instead of sucking most of your house heat up the chimney, they will actually heat the house. With a big glass door, you still get the fireplace ambience.
The only problem with mine is that the fan needed to get the most heat from it is pretty noisy.
My insert has a continuous metal liner fitted to the stove top to the top of the chimney, which is really nice for cleaning. All the debris ends up inside the stove, and you don't need to remove the stove from the fireplace to clean the chimney.
I used to have a year-round creosote smell in my house from the fireplace because it would backdraft frequently. By sealing around the stove well when I installed it, that has gone away.
Here is a link about chimney related stuff.
http://www.thechimneysweep.ca/2stackeffect.html
Has the chimney been swept recently as an unclean chimney or one with blockages would contribute to poor draw.
I don't know much about this stuff at all but hopefully someone else will help out.