You would need to notify your creditors through the official receiver handling your bankruptcy. in fact, you would leave it to the OR. when you go BR you fill out a statement of affairs in which you list as much details as you can about your creditors. the OR then contacts them. if you like you could go BR then advise your creditors of your BR ref no. so that they will desist from contacting you. there is no point in telling your creditors you are going BR BEFORE you actually petition it in the court.