Key in www.uk.cibt.com this website will enable you to key in the country you are visiting and whether you need a passport, however if you are entering by sea you will not be able to obtain Visa on arrival this is only for major airports. A one entry passport is all you require if you are entering more than once unless you leave vietnam waters.
The above is what I have found out so far as we are doing the trip in reverse.
Have a look at this site http://www.dfat.gov.au/visas/ and certainly you will need a visa for Vietnam.
And India! Egypt is confusing, If you arrive by cruise ship, no visa required. If you arrive by air you obtain a visa on landing. Hong Kong, no visa for UK passport holders.
Apologies this is the site http://www.direct.gov.uk/en/TravelAndTransport/TravellingAbroad/PassportsAndVisas/DG_4019505 scroll down to the Foreign embassies and check out each country you will visit.