Spotted...

Chap on a green beater'ish fixie fixie with white bar tape, Herne Hill > Brixton around 1000. Impeccable riding, observant and courteous

This could possibly have been me [...] Of course, it would be rather embarrassing if it wasn't, and now I look like I'm claiming someone else's good riding...

Most defo sounds like you Olly. Your courteous riding is why I have asked to ride DD together.

Nice ride in to work with Nelaii this morning. [...]
Might swing by the Roebuck later to see what the big deal is!

Nice to ride with you too, and nice to meet yet another graphic designer from here :)
And defo come to the Roe! I shall be there although not until about 7ish.