Hello.. any advice will be appreciated. I am currently in the UK on the HSMP visa and in 2012 can apply for indefinite leave to remain and then citizenship. I am pregnant with my first child and am estranged from the father who is a UK citizen. We are not married.
Will my child be a UK citizen if I am not married to the father ?

No. If the Father jointly registers the birth then he will assume full parental responsibility and the child could be registered with the English authorities thus entitling him/her to a British passport and dual nationality. As you are estranged then this seems unlikely, so the child will be registered only in the mothers name, thus inheriting her nationality.