Strictly speaking, only the 4 motion V5s and V6s have two banks of lambda probes. Hence, all UK-supplied V5s have one bank with two probes.
The fault might just be due to a dodgy connection.
I get the very occasional "slow response" error on probe 2, which seems to make the fuel economy slightly worse until I clear the fault. It's happened once or twice in the last 6 months, so I won't be getting it replaced just yet.