There is a pipe (around 12/15mm in diameter) sticking out of my house at ground level. I remember seeing water dripping from it in the past but since I had work done on the house nothing is ever coming out of it anymore.
I am wondering if it's not the drain pipe for our boiler (a worcester bosch highflow 400) which has been disconnected/broken when builders changed the kitchen floor and removed a radiator (the kitchen is located between the boiler and the external wall from which the pipe is sticking out). The reason I am worried about it is because I have started having rising damp around the boiler and in the kitchen where there was a radiator in the past.
Any ideas? What is this pipe for? Does my boiler need a drain pipe connected to the outside? Thank you.

Your boiler will have a master drain and also a safety valve that can pop off due to to high a pressure. You need to track down exactly what the drain line is from to effect a repair.