So it wasn't the ageing Flight Data Processing system. It was relatively new, well compared to the systems around it, so lack of investment wasn't the issue.
it's a system used all over the place. There are no COTS products in ATC but this one is as close as it gets.
It is the sacrificial lamb in the NATS architecture, it processes and sanitises data before it gets to the more critical systems. It does have main and fallback running the same software.