Best all British, except cables, system you heard or can think of.

Some German and French can be bright, I think.
bdp24, why not REL subs ? Should do well with Harbeth, but maybe not with QUADs
Mapman, I don't tolerate yellow badges. Please..

inna, the GR Research/Rythmik OB/Dipole Sub is a completely different animal than are sealed and ported subs, even really good ones like REL’s. It works well with all loudspeakers, but especially dipoles. A dipole sub with a dipole speaker, see? Siegfried Linkwitz designed his dipole speakers with an integral dipole sub similar to the GR Research/Rythmik, but without the benefit of the latters servo-feedback system.

Yeah, I thought so, REL with Harbeth but GR dipole with Quad.
No-one mentioned ATC speakers yet..

DCS Vivaldi stack or Chord Dave + Hugo M-scaler 
EAR 912 Preamplifier 
ATC 150ASL 

but I like many of the suggestions above too!