Can I withhold the rent if the landlord doesn't maintain the property?

The maintenance in question must be a material breach by the landlord such as no water / electricity, a burst geyser or non-working oven. A material breach does not include missing internal keys, blown light bulbs etc.

If the landlord fails to remedy a material breach you should cancel the lease and vacate the property or take legal action.

If you withhold rent, you yourself are committing a material breach and the landlord can take the necessary action to collect the rent - cancellation of the lease, court order eviction or blacklisting on credit bureaux.