Thanks guys - I have never added the additional liability insurance on any US car hire and it doesn't include it if I book via the US or UK

Adding the optional all singing all dancing liability is $33 a day.

In fact as I do not include any extra insurance and decline the following as standard on all US bookings.....

Loss Damage Waiver:
Liability Insurance Supplement:
Liability Insurance Supplement (Only applies to car hire commencing in California.):
Personal Accident Insurance/Personal Effects Cover:

The cover for both is identical AFAIK.

Maybe some basic liability insurance is covered anyway?