You ask at the local council office who keep the record of trees with orders on them. By and large, a protected tree can be cut down without prior permission if if is dead, dying diseased or dangerous...but you would need to prove that it had been. Implications would depend on who made the decision to cut it down...if you came into my garden and I wasn't there and cut down one of my protected trees then I as the landowner wouldn't be responsible....provided i could prove that i hadn't said "you can cut it down tomorrow, I won't be there!" repercussions in Hampshire are usually fines