Explanation:

- Option 1: "was under"

- Implies past tense.

- Suggests the scrutiny by the High Court occurred in the past.

- Context may not fit if scrutiny is ongoing.

- Option 2: "under"

- Typically requires a verb for completeness.

- Incomplete phrase without context.

- Option 3: "is under"

- Implies present tense.

- Suggests the demolitions are currently being scrutinized.

- Correct for ongoing scrutiny.

- Option 4: "however under"

- Grammatical inconsistency.

- Lacks a preceding statement to contrast "however."