Was the ETO production with Britten's original orchestration, or one of their "scaled-down for touring purposes" versions?
It's been a while since I saw the score but I'm pretty sure Britten's original orchestration is already pretty small, maybe double winds and certainly very few strings although the option's there to do it with full strings, as he did in his recording.
Ah, here it is:
Scoring
colS,S,M,A,CT/A,3T,2Bar,BBar,3B,acrobat speaking role; children's roles: 4Tr,chorus 2(=picc).1(=corA).2.1-2.0.Dtpt.1.0-perc(2):tgl/cyms/tamb/gong/2wdbl/ vib/glsp/xyl/tamburo/SD/TD/BD/timp/2bells-2harps-hpd(=cel)- strings (min 4.2.2.2.2)-Stage band:sopranino recorders/cyms/2wdbl
2 flutes, 1 oboe, 2 clarinets, 1 bassoon, 2 horns, 1 (D) trumpet, 1 trombone, 2 percussionists, 2 harps, harpsichord/celesta, 4 first violins, 2 second violins, 2 violas, 2 cellos, 2 basses in case that isn't clear from the hieroglyphics