My artner as 2 of my daughters living with him as tthere schools etc are where he lives . I have our 3 and half year old living with me . We have been split up 11 months and my daughter only knows this as her home and pre-school . Can my ex take her off me

If he files for custody and is granted it by the court. As would be true in the case of any parent involved in a separation or divorce.

my artner as 2 of my daughters living with him as tthere schools etc are where he lives . i have our 3 and half year old living with me . we have been split up 11 months and my daughter only knows this as her home and pre-school . can my ex take her off me

Wait a minute... why are two of "your" daughters living with your ex? Is he their biological or legal father? If not, then there is no grounds for them to be living there. If yes, then your ex has "two of OUR daughters" living with him, not "two of MY daughters."

I don't know what you mean by "take her off me" - are you asking if he can become the primary custodial parent? Yes, only by court order. Odds are he wouldn't be successful, so long as the child is being well taken care of. You said you've had her primarily for 11 months; unless she's being abused or neglected in some way, the courts will most likely not want to uproot her from her familiar surroundings.