The details you need are
here in section 4.3.9 to 4.3.11
quote:
4.3.9 Qualifying fare levels for Economy to Premium Economy upgrades and Economy Companion tickets on Virgin Atlantic flights.
Only full adult fares apply:
Country of fare origin Qualifying fares Exceptions
UK Y,B,L Flights originating from London to Tokyo exclude L class
Japan Y,B,L,M Flights originating from Tokyo to London include M class
Caribbean Y, B, L
USA Y,B
Hong Kong Y, B, L Flights from/to Sydney from/to Hong Kong exclude L class
China Y, B, L
South Africa Y, B, L, M
Nigeria Y, B, L, M
India Y, B, L, M
4.3.10 Qualifying fare levels for Premium Economy to Upper Class upgrades and Premium Economy Companion tickets on Virgin Atlantic flights:
Any full Premium Economy fare booked in W or S class. Excludes APEX and Excursion type, seat sale or any other special/promotional type Premium Economy fare. K class fares for travel originating from Hong Kong do not qualify.
4.3.11 Qualifying fare levels for Upper Class Companion tickets on Virgin Atlantic flights:
Any full Upper Class fare booked in J class. Excludes Z Class APEX and Excursion type, seat sale or any other special/promotional type Upper Class fare.