I believe SBS-1 can pick up most GA stuff, whereas I’ve heard a whisper that Air Nav Radar Box can’t, is this true?

There is no requirement for GA in the UK to fit Mode-S transponders before at least 2012 and maybe beyond that, and currently no requirement even beyond to fit ADS-B. Until both are done, GA (or any other a/c not carrying the kit) won’t plot on the “radar” of either SBS or Air Nav.

A