Reaching Unst, the northernmost inhabited island in the UK, already takes a chain of ferries through Shetland's inter-island network - and that same remoteness is the honest reason travel insurance is worth carrying here rather than any particular danger around Baltasound, the island's main settlement.
Unst has only basic local health services, and anything beyond routine care means a transfer south to Lerwick, Shetland's main town, for hospital treatment. Genuinely serious cases are typically then referred further, by air, to Aberdeen on the Scottish mainland, the real specialist hub for the Northern Isles. A patient too unstable for the ferry crossing may instead need air transport directly off Shetland, weather permitting, which underscores why medical evacuation cover matters here as much as ordinary treatment cover. Confirm your policy covers medical transport between island and mainland facilities, since that referral chain, not treatment on Unst itself, is the part most likely to involve real distance and delay.
Reaching and leaving Unst depends on that same chain of inter-island ferries connecting Yell and the Shetland mainland, and North Atlantic weather regularly delays or cancels sailings with little notice, particularly in autumn and winter. A missed connection can strand a traveler for a night or more on either end of the chain, which is where trip-delay cover earns its keep on an itinerary built around this kind of remote island travel.
Keep any clinic paperwork from Lerwick or Aberdeen, ferry-cancellation notices, and receipts for unplanned accommodation if a crossing is disrupted. Check whether your existing health cover extends to the UK specifically before relying on it, since the rules for visitors differ by nationality and this page cannot determine what your own plan includes. Many policies treat weather-related ferry disruption as a standard delay claim, so confirm the wording before you travel this far north.