Notices displayed by TfL at bus stops say: "From Saturday 2 December, we are making some changes to the frequency of our services on route 381, which runs between Waterloo and Peckham.
"Buses on this route will run every 12 minutes instead of every 10 minutes during the daytime on Monday to Saturdays.
"Buses will continue to run every 12 minutes during the evenings and all day on Sundays."
TfL's website included an extra note to say that the 12-minute frequency applies all day "except before 0630 on Monday to Fridays and 0830 on Saturdays when buses will run every 15 minutes and on Sundays before 0930 when buses will run every 20 minutes".
The change means that parts of Southwark Street - previously served by both the 381 and the withdrawn RV1 route - have seen the weekday daytime bus frequency cut by 58 per cent in the past decade.
In 2013, both the 381 and and the RV1 operated at a 10-minute frequency, giving a combined service of 12 buses per hour.
Now the same streets receive just five buses per hour.