wrote:
I live in a 1st floor flat and have an overflow pipe which is slowly
dripping outside. The pipe is white, about 1 inch diameter and exits
the building at floor height.

I suspect that it may be my immersion heater or bath. Could someone
help me out?

The immersion heater has 2 electrical cables each connecting to a
seperate power switch on the wall next to it. The top switch on the
wall is on and the red power light is on. The bottom switch is on but
the red light is off.

I've also noticed that my bath takes over 10 minutes to empty about
10cms of water. Could this also be a candidate for my problem?

What about your toilet? Have you checked the cistern? Might be that
simple.

Bath overflow normally goes back into the drain.