Aphids/Sunburn/something else?!? Please help

I'm new to gardening.
I have a small urban garden in South London. It's a walled concreted garden and I broke up some of the concrete to install a raised bed earlier this year. 
There's a sycamore just outside the garden that hangs over. 

All of my plants were thriving. Then I started having massive showers of sycamore flowers into the garden. I was picking them out of the raised bed and containers daily. Last weekend I noticed some green fly. I purchased some adult lady birds and the arrived last Monday. Unfortunately within a few hours of setting them free they were all gone except for one!  

I set about researching aphids and discovered the aphids I have are probably sycamore aphids, and the flowers landing in the garden is probably attracting them. (Although I do intermittently see blackfly and white fly too). And that the ladybirds probably all flew up to the aphid party in the sycamore tree!!!!


I don't have huge infestations of them, on inspection I can find up to 10 flys on several plants per day. I didn't want to become overrun with them so I did a soapy water mix (dish soap) and sprayed all the leaves front and back. 
Within half an hour I noticed my lavender had several wilting/brown leaves (prior to this it only had 2 leaves affected by leaf miners, but was otherwise very very healthy). 
The next morning I came down to several plants with brown damage on their leaves. I went to my local garden centre and showed them photos asking for advice. She thought maybe the heat had caused the water to evaporate and then the concentration of soap was too high causing damage. 

The next day the damage was significantly worse so I brought in my begonias and they thought it was sun damage caused by me spraying while it was sunny (a mistake I wont make again!!!!!) 

This is what several of my plants look like today. The brown damage continues to get worse. Its not effecting all the plants in the garden to the same extent, but it is affecting plants of several different species, so I thought a fungus/virus was less likely. 

Is this still the ongoing effects of the sunburn caused by my spraying? Or is it something else?!? On the fox glove the patches have gone from brown to translucent. (It's worth noting the foxglove buds are continuing to develop and grow) But on the begonias the darkening brown leaves are shriviling up...  

Please help!!!!!