Synopsis Great Britain is building what was billed as the most advanced En-Route Air Traffic Control system in the world at the National En-Route Center (NERC) in Swanwick, Hampshire, to control traffic in the London Flight Information Region (FIR), which covers southern British airspace. The £350+ million system has run into problems, experiencing successive delivery delays, and some scaling problems. The contractor was also building the U.S. AAS system before it was cancelled, and I understand about 1M LOC (out of 2M OLC total) are being reused. I wrote a short note entitled Software problems with new-generation air-traffic control center about the problems as reported in a Flight International article in May 1997 for RISKS-19.18. A further comment by Andres Zellweger appeared in RISKS-19.23. Having been briefed by Bob Fletcher of NAV Canada concerning the new Canadian system, CAATS, and Bob Ratner (Ratner and Associates) and Bob Peake (Airservices Australia) on the new Australian system TAAATS, I wrote a memorandum to the Transport Subcommittee of the House of Commons, who were considering the question of NERC on 19 November, 1997, expressing my concern and giving my reasons. Subsequently, I was invited to give oral evidence before the Transport Subcommittee on 11 March, 1998 on the issues (a) how long an audit, the purpose of which would be to determine if the system could be made to work and when, would take; and (b) whether Sir Ronald Mason's assertion, that dual-sourcing is a `basic principle' of safety-critical system development, applied to the case of the new twin centers NERC and NSC (the New Scottish Center to be built in Prestwick) and therefore that the NSC contract, awarded to the same contractor as NERC, should be awarded instead to another contractor. My written evidence to the Transport Subcommittee expresses my views, and those of some colleagues, on these two issues. The Environment, Transport and Regional Affairs Committee's Report recommended inter alia a technical audit of the NERC system, to determine whether it can be made to work; to assess the safety of the current operation; whether traffic growth has been underestimated; and whether dissimilar systems should be used at NERC and its future companion NSC in Scotland.