Yes and no.
I have found most drivers more courteous during lockdown, but some who are taking advantage of the quiet roads to go as fast as possible. However most of my riding recently has been on obscure Cotswold lanes, so a bit different from SE London.
Partly I think it is that there are a lot more cyclists and walkers around, so they have to go a bit more carefully. As a cyclist I am being more cautious on the lanes, since I know there is likely to be a group of walkers around the next bend and it is difficult to stop quickly on the sort of gravelly potholed surfaces we have here. On the other hand I have had a few unpleasantly close passes. However all the bad driving seems to be on the more major roads, presumably where they think they can get away with it.
As an illustration, something almost unprecedented happened to me a couple of days age. Whilst going up a steep hil I met a 4x4 coming down, and he immediately reversed back to find a passing place. Admittedly I wasn't going to stop on such a steep hill, and his car was so wide there was no way to get past where we met, but even so that was remarkable behaviour. Let's just hope it continues.