I don't want anything apart from a system that works, albeit at a reduced capacity during a disruption
Would 90% be enough ?
compensation to the airlines
The NATS charging regime does include penalty payments for delays. It's extremely complicated but full details are in the public domain, just search the CAA site for NATS Licence. The penalties are primarily to ensure that NATS doesn't sweat the assets though.
the back-up system could be brought on-line with a flick of a switch
What if it is the switch that has gone wrong ?