Just for the avoidance of doubt the system that failed last week was not a £100M system. The budget will have been much more modest than that.
I don't know the tendering arrangements. As a technology refresh of an existing system single tender might have been appropriate, or it might have been widely tendered.
They may have been living the high life at NATS expense but as they were bought out of receivership around that time I think it's unlikely.
The hardware requirements for these systems are quite modest & it's possible they were a separate tender. Even pre Brexit buying hardware from the UK shipping it to another country for integration & then shipping it back was a nightmare. I shudder to think what it's like now.
The amount of fallback wouldn't have been hidden from NATS. Everybody would be very aware that there was no software redundancy. We will need to wait for the next report to find out why that was thought to be Ok.