Good evening. Long term reader and seldom poster here!

I am trying to book a return flight with car hire and the car hire doesn't show options to add additional driver(s) or to add car seats, etc.

I start by looking at flights
Once I have the price, I select the option to look at car hire
I select the car
It takes me straight to the confirmation and basket

How am I meant to book the seats, etc?

The only thing I believe could be causing this is booking a different class outbound to return?

It also looks like I lose the discount from booking together.

Has anyone else experienced this and got a solution? Is calling BA even a real option now and, if so, would they be able to resolve?

Any help appreciated.