Hi Karen
Sorry I haven't replied earlier but I have been in the Azores for the last week.
I have been insuring with Staysure for a few years. My current policy covers emergency medical and repatriation expenses up to £5m for basic cover and £10m for comprehensive cover (my prefered option). As far as I can remember that is what cover I had for the Antarctica trip. I didn't try to find unlimited cover as I thought £10m was more than enough.
As I recall I spoke to the company about a single trip policy for Antarctica but it actually worked out cheaper by a few pounds to purchase an annual policy - I still can't understand how that works!
The trick is to check the cancellation and curtailment limits on a prospective policy as well as the medical and evacuation coverage limits. A lot of policies don't go above £5,000 per holiday at best so you need about £10,000 of cover on this trip - more if you've upgraded cabin or flight classes as I did - to cover you for any ill-health or immediate family or dependant bereavements that stop you going on the trip at short notice.
Some policies will either not pay out at all if you are undercovered, and most will apply a dirty trick commonly used in domestic buildings and contents insurance and apportion the undercoverage off the claim / limit. i.e. let's say you had £5,000 of cancellation cover but the holiday cost £10,000. You might think you could get £5,000 back. Wrong. The insurer will say you were undercovered by 50% therefore you only get 50% of the coverage limit - so £2,500 back instead! Most people don't know that this is what many insurers do in that situation.
Also, I had one insurer say that don't cover holidays booked more than a year in advance - which cruises often are.
I'd recommend reading the full Ts&Cs of a prospective policy in detail before buying it; don't buy just on the sales pitch bullet points of the cover alone. It took me four goes to find a policy that once I'd scratched under the surface actually would have paid out in full for this cruise in at least half of the claim categories.