I have been looking at spring hinges to BS EN1634 to replace existing butt hinges to flat entrance doors to up-grade to self closing. Would this be acceptable and not interfere with the fire rating of the existing door.

I am not sure what you have been looking at but BS EN1634 is the standard for fire resisting doors, BS EN 1154:1997 is the standard for self closing devices?

Check out http://www.firesafe.org.uk/fire-door-fitting-and-ironmongery/ and http://www.firesafe.org.uk/fire-doors/

we have perko door closers fitted to our flat doors do we need overhead closers fitted as well?

You should not normally require overhead door closers as well, as long as the units work well and reliably close the doors fully. There are a number of different Perko door closers, though, with varying levels of certification.

Both Perko and Astra offer basic concealed door closers claiming to be compliant to the relevant standards. The upper end of concealed door closers, such as Perkomatic and Powermatic have actually been certified.

Harry

i have been asked if the existing srung loaded hinges marked BSEN 1634 can stay on the door after disengaging the spring action and fitting an over head closer to bs1154 , or should these hinges be changed to hinges marked BSEN 1935 grade 13 ?

Assuming its a timber-based door - If you are able to consult the installation instructions or data sheet for the fire door leaf you can check that the existing hinges are suitable.  If you cannot trace the door leaf manufacturer to do this and the hinges are in good condition you could retain them, although personally I would change them because most timber fire doors have a limit on the dimensions of the hinge knuckle.