Thanks for the various words of encouragement, I'll persevere with the
washing-up liquid for a bit longer. I do notice quite a lot of
ladybird hanky-panky going on on the plant, so I have been surprised
at the small numbers of offspring. Anyone got any suggestions for
spotting ladybird larvae and avoiding wiping them out along with the
aphids? Or maybe it's better not even to use washing-up liquid and
just to let the ladybird larvae get on with it.

I'm in inner London by the way, if that makes any difference - not the
most natural of ecosystems in the first place. Slugs and aphids seem
to have inherited this part of the earth.

Cheers!

Martin