The gerbils are so damned talented!
So glad for all the good news.
It turns out that my neighbour was getting very analytical about our landscaping because she really likes what we're doing and wants to do something similar!
And her discussions about planning permission are so she doesn't have to do the research herself.
I have been tearing my hair out having fun interpreting what an elevated platform is in planning terms. If it's more than 300mm above the original natural ground in a conservation area, it needs planning permission. The slope of our garden from the back fence to the house is a whopping 450mm! So building a patio that is level involves building two patios - an upper patio that is level with the back gate and a lower patio that is level at the house, with steps between them. This makes the upper patio 350mm above the lower patio.
But the measurement is not to the patio, but to the nearest original natural ground.
The slope is so severe that the bit of the upper patio closest to the house has to be built 200mm above the original natural ground, but that is within the tolerance. The slope continues down to the house where the lower patio level is level. So the difference is not 300mm.
It's been worrying and complicated but the end result is we don't need planning permission. We do need it to stop raining though.