Ok I got a bit of a headache here....
Here are my current membership details:

Tier points: 560
Flights: zero
Tier points collection year ends: May 8, 2021
Base airport: GVA

So have enough TP for Silver but I'm missing 4 flights, which is easy enough to achieve in normal times but my question is: can these 4 segments be flown only on BA? Or would IB flights work too?
And for BA, 2 flights means a return trip correct? one out, one back. I could achieve 4 by doing a, for example GVA-A-B and B-A-GVA?

It would be easier at this point for me to book a turnaround flight to Spain or even Portugal on IB rather than to the UK on BA. Unless turnaround flights do not require PCR tests in the UK?