Up until now, I've tried to warn you of the problems that the police might face in taking any action against this man. [i.e. it would be difficult to prove 'coercion' relating to the suggestion of intimate acts and it might be hard to prove harassment in relation to his pursuance of the (alleged) debt]. However, if you've got evidence that he forged your signature, in an attempt to withdraw funds from your account, there are no 'grey' areas here. Quite clearly, he has committed a criminal offence and the police would be able to bring him before the courts.
If we accept that a debt exists (or that the photographer genuinely believes that a debt exists), he has the right to pursue you through the civil courts. What is rather surprising is that he has not sought to use the small claims procedure. Instead, he is seeking to make you bankrupt. A statutory demand can't be served by e-mail. It has to be served in person. So he might only be bluffing. If you do receive the demand (and don't pay) he will be able to petition the courts for your bankruptcy. However, he can only do so based upon your inability to pay. If the debt is contested (e.g. you state that you don't owe him anything) the bankruptcy court would require that the matter should be resolved (for example, by the small claims procedure) before they would take any action towards declaring you bankrupt.
I suggest that you definitely report the guy to the police with regard to his attempts to forge your signature. Additionally, they might think that his threat to tell your employer about the matter could amount to 'harassment for debt'.