What steps do I need to take to teach.....?

Some universities will allow you to "convert" your 3D design HND to get you onto the second or even third year of a degree course and then you'll need to do a PGCE to gain qualified teacher status. Your question doesn't say what you've been doing since 1999 but if you've been out there and gained an industrial experience then you don't need a degree to teach post 16's in a college and just a teaching qualification may do.