Probably photographic identity such as a passport or suitable driving licence.
Requirements depend on the ferry company.
Yes you do, even the travel to Ireland from the UK has now been restricted to passport holders only.
No
No but you will need photographic identity. Check wit the ferry company.
yes you do in order to travel you must have a passport
Strictly speaking, you won't need any ID to get on the ferry from Portsmouth to Guernsey. However, if you are not a British citizen, it might be best to take your passport with you.
No.
No but you do need I.D.
no - it's an internal UK ferry trip
That would depend on where you are travelling from and your nationality. If you are arriving from mainland Europe you will need a Passport to enter. Anyone leaving the Country and returning needs a Passport.
For a ferrytrip from England to Amsterdam, the Netherlands, a passport is needed. During the trip, the border between the two countries is going to be crossed.
It depends where the ferry is going. if it is a foreign country, then yes, you will need a passport. If not (ie its an island belonging to the country you're leaving from) you don't.
You don't need a passport as such but you will need an identification document with a photograph. Other documents such as a driving licence may be acceptable. This is not for entry to the Channel Island but to identify yourself to the air or sea ferry company transporting you.