I'm currently doing an MSc research project which I'm really enjoying. There is a PhD vacancy in the lab I am working in. However, I'm debating if doing this PhD would be the right choice. Does it look bad on a CV if a student does thier MSc and PhD in the same place? Is it better to take time out in between to get experience/develop interests? I was not planning on doing a PhD straight away and I also had other PhD topics in mind. But this is a fantastic oppourtunity.

if you did your first degree at a different uni then it is fine to do the msc and phd at the same place.

It actually shows that you were good enough for your supervisour to really want you to stay on. It looks like a good thing, not a bad one.