I am living in a converted flat consisting of 2nd and 3rd floor of a property and all the interns doors and entrance door had consealed self closer installed. Since having a baby we removed them all as they were very dangerous with a moving baby. Now that we are selling the flat, do we need to reinstall them? Would that require say for surverying purposes?

Current building regulations removed the requirement for internal doors to have closers so they are OK, but it was incorrect to remove the front door closer and you will need to put that back.

You said a concealed self closer installed to the front door, if it is not a perko powermatic, then it is unlikely to meet the required standard and you will need to fit an overhead self closing device to BS EN 1154:1997 Building Hardware – Controlled Door Closing Devices. Check out https://www.firesafe.org.uk/fire-door-fitting-and-ironmongery/.