Paul Corfield wrote:

The most surprising (to me) aspect is how busy
Sunday services are - I've been out most Sundays recently and many buses
are full or near to full which is a big turn round from about 10 years
ago when demand was much lower.

Sometimes too full - how often are Sunday services reviewed and potentially
expanded?

One particular problem I've seen is the over reliance on existing bus routes
to double as rail replacement services. The Central Line betwen Mile End and
Stratford is the most obvious case in my normal routine and often I've found
the 25 ridiculously crowded (even by its standards) and insufficiently
frequent when there's no tube between those points.