FlyerTalk Evangelist and Ambassador: The British Airways Club
Join Date: Jun 2008
Location: Somewhere between 0 and 13,000 metres high
Programs: AF/KL Life Plat, BA GGL+GfL, ALL Diam, Hilton Diam, Marriott Gold, blablablah, etc
Posts: 33,183
Do you mean LHR-SYD // GRU-LHR (as open jaw) or LHR-SYD-GRU-LHR (with SYD-GRU operated by another airline)? If the former, no issue, if the latter, you need to call BA and ask as it will include some non-BA flights which may be an issue.