"Quite a few 1st horns in London still managing to stay away from the dreaded F alto (or Eb alto)."
What's the problem with first-horns using altos? (Or triples, for that matter.)
The instruments are never single F alto horns and the majority of the time are played on their Bb side - like a double would be.
Mind you, years ago some die-hards condemned double horns. A bit further back, horns with valves were regarded with suspicion.
See John Cerminaro's claim that the triple is the horn of the future -
http://tinyurl.com/mkj9hq5See Frøydis Ree Wekre's scepticism about Cerminaro's article (and about altos) -
http://tinyurl.com/lvzyg7o