Nimrod AEW radar
I remember that the British computer used was the GEC4080
a not very powerful thing usually used for process control. The
AEW radar was Synthetic Aperture which necessitates quite a computational effort.
Also quite a lot of processing was needed to remove Ground Clutter.
It was obvious at the time that the 4080 was not powerful enough.
Other sufficiently powerful but non-british computers were available, but not made in-house.
So indeed buy British, but only if good enough.
Please correct me if you know differently.