Londongirl,
I'll be talking from personal experience. Been there but survived it. I DO NOT mean to sound lecturing.
Nothing good will come from the situation when you are paranoid like this. You lose control and you can't think straight. When this happens, you are bound to make mistakes and in this business mistakes might cost a lot. So to begin with, take a break just as Violette said. Even if it's just a week-end at your parents.
Secondly, see if you can arrange it with your agencies to be able to call a potential client before they give him your address - along the lines of "this particular lady likes having a chat with her clients beforehand to see what you're looking for so she could be totally ready to meet you" (and most guys will be happy as, like you, they don't know who they are going to see) and then you can call the guy withholding your number and take it from there instead of turning him off at the door - this will infuriate both him and the agency.
I know Violette meant the best for you (and in no way am I stepping on your toes, Violette, but as a qualified herbalist I know that it's a common mistake) but do not take St John's Wort. First of all, it's not a relaxant, it's a stimulant - it's prescribed in depression to make you move. In your state, it's not going to help. Also, it interferes with the effect of the pill (if you take it) and you might want to avoid it. I'd suggest Oats or Passion Flower. You can get Oats glycerol from Holland and Barret (around 5 pounds) or Passiflora complex by A. Vogel/ Bioforce from most other health shops (8-9 pounds). Either will help take the edge off (but your mind may still be going) but it's only a temporary measure as it doesn't treat the cause. For me, hypnotherapy worked a treat and it only took 2 sessions.
Another thing is to try and stop concentrating on the negative. I believe with my whole heart that what you focus on, grows - and it works every time - so when you focus on something bad, guess what grows? Maybe that's why your recent clients looked dodgy. Or maybe, considering how scared you are, you were just reading too much into their actions/ words.
There's another thing I can suggest. When I worked in London, I sometimes used a flat in Victoria for incalls. I know it's not Baker Street, but if you find nothing else, I can give you the phone number for them.
Now, talking about your neighbours and your landlord - you might not believe this, but people who will suspect you of being a sex worker are either regular punters or other escorts. Normal people don't even think about things like this. Even if your neighbours do notice a lot of men coming and going, they will most probably think you are just a promiscuous woman. Or a drug dealer

And even if your landlord does find out, he won't necessary kick you out, he might want to come and visit you

or just raise the rent. And even if he does want you to go, wouldn't it be good? It gives you a chance to find a better place with better neighbours.
I once worked from a flat that I rented through estate agents and a "friend" of mine was kind to call them and inform of what was going on. So one day I received a letter from them saying that they knew and could I please get in touch with them. This was probably the worst day in my life. Mentally I started packing, but it wasn't the move, it was the conversation that I dreaded. Pulled myself together and called them. As you know, attack is the best form of defence, so I said - are you threatening to kick me out? And the manager went "no-no, not at all, it's just that we were told, but you are definitely staying!" And that was all!
There are a few more things I have to say, but the post is already too long and I can hear you snoring, so I'll shut it, but do let us know what's going on and how you're coping. Best of luck to you.