OP, my advice would be to ignore Leave - you don't have to explain yourself, your dates or your decision to have sex to her or any of us. I for one am not here to make you feel any worse about your situation.
Yes let's ignore the person asking the pertinent, awkward questions shall we? She won't be able to ignore SS when they ask exactly the same questions. Do you honestly think the cheap thrill of making someone feel worse about a shitty situation is my sole motivation here? 
There's sympathy and then there is useful constructive advice.
But apart of me knows what will happen if I go through the pregnancy (eg. Social services being involved again, I wil get depressed, Not giving much attention to DD's special needs).
SS have supported me for many years, due to the DV between the dad and I and even though they were helpful, it was very stressful. The questions, the assessments, I was depressed, I wanted them to leave me alone.
it all got to a point it that the violence was becoming frequent and they did kind of say that if I got back with him again there's a possibility that DD will be removed from my care.
I feel like they have given me many chances not to go back out with my ex, but I kept on going back to him. I have finally left him for good, but I think if they found out that I am pregnant by him. I fear that my DD and the baby will be under a child protection plan and sooner or later a court order to potentially remove them.
Itsacold I'm not sure SS will agree that you 'finally left him for good almost two months ago' given that you appear to be 2-3 weeks PG. The simple fact is that both of those things can't be true. Even if you are further along in your PG than you thought, for the midwife to even think you might be 2 -3 weeks PG you must have told her you slept with him very recently, and certainly since you 'finally left him for good'.
SS have heard it all before - what makes you think they'll believe you this time? Let's remember, this isn't about what you think about the current status of your relationship, it's about what they will think.
People can get annoyed with me for pointing this out if they like, but ignoring it won't help you when SS come calling.
I think perhaps you were hoping that people will tell you lots of positive stories, tell you everything thing will be fine, SS will leave you alone, you'll cope admirably with your PGCE and your depression and a new baby as a lone parent and a child with SNs and possibly the constant hovering presence of an abusive ex, while living in temporary accommodation with friends and having your family's disappointment and disapproval to contend with.... But the truth is it WON'T be fine. It will be a massive struggle and if you can't stay really really strong and jump through all of SS's hoops, it could end in you losing your children.
First of all, forget what you want for a moment, is any of this fair on your DD, when you both have a chance of a fresh start with no more SS intervention?
Can someone please tell me, regarding social services, what will
Happen if I have another baby with someone they know of, who is abusive.
I think you know what will happen. You've been told by them before what is likely to happen. You've already answered your own question up there. ^
It seemed to me that the knowledge of that, and the spiral of stress and depression it might send you into, was the MAIN REASON you posted for advice about whether to terminate or not.
That's why i said 'you pays your money and takes your choice'. It's up to you, of course. There is no point in me telling you what I think you should do, but if you go ahead with the PG then don't go into it without being completely honest with yourself about the reality of what lies ahead.