My veneer is slipping down and the gum above my tooth is very red and almost looks cut, it isnt painful but surely not normal?

If any type of restoration is placed too close to the connected
gingival tissue, inflammation will result. This may be what is causing your
inflammation, and the veneer would need to be removed or adjusted by your
dentist.The other concern I have is the smell that you
mention. If you’re just now noticing inflammation and a foul smell after having
had your veneer for almost a year, there is most likely some type of gingival
infection (such as periodontal disease, or impacted food) that is causing this
condition. Your hygienist or dentist can clean under the gum pocket to remove
any tartar buildup and help the area heal. If periodontal disease is present,
the tooth may be lost if treatment is not sought out in a timely manner.

Based on your description, it appears your veneer is causing inflammation of your gums. When porcelain is placed on teeth it must be a minimum distance from the bone level and maximum thickness toward the gums. This is called biologic width. It sounds like your veneer may be violating the biologic width causing the gums to grow puffy and inflammed. If this is the case it may be corrected by thinning the width of porcelain or by recontouring the gum/bone by a crown lengthening procedure. Have a consult to have this area evaluated.