Agrressive Behaviour

Question
My 7 month old male English bulldog is a friendly sweet dog until we try to put a harness and lead on him. He then snaps and becomes so aggresssive that we can't continue. He has never liked his lead but allowed us to put in on and go for a walk. He only started the agressive behaviour yesterday. I tried again this morning and same thing, he growls, snaps and then tried to bite me.  How can i change this behaviour without getting myself bitten?

Answer
This appears to be a fear related behavior (dominance aggression at 7 months is unheard of in that breed so let's hope it's fear).  Active dog to human aggression needs the in person evaluation of a certified applied animal behaviorist.  From the spelling of "behaviour" I'm guessing you're in the UK.  Contact the Association of Pet Behaviour Counselors (I believe they have a headquarters in London and can direct you to a member located near you.)  Meanwhile (until you're able to locate a specialist) leave the harness on the dog with a short, lightweight leash attached (to which you can then attach, using the handle at the end, a longer lead for walking.)  Do NOT provoke an aggressive response (as each time the dog uses aggression in a successful manner, it learns more about aggression.)  when you next attempt to take the dog out using the leash, observe the dog's body language and presentation; if he demonstrates fear or aggression (tail set, ear set, growling, etc.)turn your back on him, count to ten, and start forward again.  The moment he follows with no sign of fear (or grumbling), praise and toss a small treat, then proceed further.  Observe closely what sets him off once you are leading him.  This is a strong clue regarding the cause of this behavior.  Do not attempt to address this situation without the help of a specialist.