Concept: Private nuisance is an unlawful interference with a person's use or enjoyment of land or some right connected with land.
Step 1: Check encroachment on neighbour's land.
Encroachment on a neighbour's land interferes with the neighbour's property rights and may amount to private nuisance.
\[
A = \text{Private nuisance}
\]
Step 2: Check entering into someone house without permission.
Entering into someone's house without permission is generally trespass, not private nuisance.
\[
B = \text{Not private nuisance}
\]
Step 3: Check direct physical injury to neighbour's land.
Direct physical injury to a neighbour's land affects the use and enjoyment of land and may amount to private nuisance.
\[
C = \text{Private nuisance}
\]
Step 4: Check interference with quiet enjoyment of land.
Interference with quiet enjoyment of land is a classic example of private nuisance.
\[
D = \text{Private nuisance}
\]
Therefore, the correct answer is:
\[
A,\ C,\ D \text{ only}
\]