If it's not the scheme you can apply to get back 3 times your original deposit ( might be 2.5 times deposit) but by law it has to be in the tenanacy deposit scheme of which I think there are 3 in the UK

 They rely on you not knowing the law and your rights

Tell him that he can go fuck himself and point out how much trouble he will be in if he doesn't stop fucking around.

I'm assuming he doesn't have the info needed to actually blackmail you - like your mum's telephone number. So fuck him. And of course he can't do a goddamn thing to you in regards to your child.

PLEASE tell me that he has said these things in writing! If so, then he is in sooooo much trouble.

The fucker should have put your deposit into a protection scheme account. That's the law. And trying to blackmail/extort more money from you is not going to look good at all.

I'm not sure if you actually need an "escort-friendly" solicitor. You only need a solicitor. In fact, I'd recommend that you start with Citizen's Advice and/or Shelter.

At the very least, he will never get an extra fucking penny from you.

Please stand up to this cockwaffling cunt and make him sorry he ever thought of taking advantage of a woman just because she's a prostitute.