Originally Posted by ISTFlyer

I am not sure about the exact loads but it should be transfer pax from Portugal, Italy, Spain, etc... that are currently flying the LHR-GRU route.
Plus, it's the only operating BA route to South America so there should be onward transfer pax transferring to LATAM flights.

I am not sure if BA would operate GIG in January, most likely not.
Though if your GIG flight gets cancelled, BA would rebook you via GRU and then to a domestic LATAM flight.

By the way, if the UK travel corridor list does not have Brasil, you would need to self-isolate for 14 days after your return to the UK.
At the moment, Brasil is not in the travel corridor list of the United Kingdom.