My son is planning a rtw. There are prices ex UK for peak or basic season for lONEx FARES. I have searched in vain to find how these are applied.

Do all tickets in the itinerary have to be in basic season for the country in which each flights originate, or are just the seasons of the country of origin relevent?

There is apost from christep which gives the season dates as follows:

Ex-Australia
PEAK 28MAY-15AUG, 03DEC-24DEC
BASIC 01JAN-27MAY, 16AUG-02DEC, 25DEC-31DEC

Ex-New Zealand
PEAK 01JUN-31AUG, 11DEC-31DEC
BASIC 01JAN-31MAY, 01SEP-10DEC

Ex-United Kingdom and Ireland
PEAK 01JUL-14AUG05, 10DEC-23DEC05, 01APR-15APR06,
01JUL-14AUG06, 10DEC-23DEC06
BASIC 17MAY-30JUN05, 15AUG-09DEC05, 24DEC-31DEC05,
01JAN-31MAR06, 16APR-30JUN06, 15AUG-09DEC06

Advice appreciated.