83,000 (we would expect sundays to be lower, people have less reason to LFD, and hospital testing less due to lower regular admissions - the "same day" tests. PCR processing is often a little bit lower. So this fall does not mean cases have peaked. [*]
However, London is certainly not accellerating, and unless there's a load lost down a sofa, it's unlikely that the 17th and even the 16th will go above the 15th. That still can be an artifact of testing (e.g. lack of test capacity, lack of LFD's for asymptomatic catching) but it certainly indicates that the rate has slowed.
[*] I hope that avoiding sarcasm enough!