Can my insurer hike my premium at renewal without explanation?

Insurers generally do have commercial freedom to set their own premiums and adjust them at renewal based on their own risk assessment and broader pricing considerations, meaning there isn't necessarily a strict legal requirement compelling an insurer to justify every renewal price increase to you in detail, particularly where the change reflects general market conditions or broader shifts in the insurer's underwriting approach rather than something specific to your individual claims history. That said, insurers regulated under the Insurance Distribution Act, Chapter 487 of the Laws of Malta, are generally expected to act with a reasonable degree of transparency and fair dealing toward policyholders, so it is entirely reasonable for you to formally ask your insurer, or your broker if you used one, for an explanation of the specific factors behind the increase, and a significant unexplained jump with no apparent driver from your side is exactly the kind of situation worth actively pushing back on and querying. Since insurance pricing does vary meaningfully between providers, rather than simply accepting a large unexplained increase, it would be worth using this renewal as an opportunity to shop around and compare quotes from other insurers or through a broker, since a significant increase from one insurer doesn't necessarily reflect where the wider market for your specific risk profile currently sits.