Transport for London is to reduce the service on bus route RV1 - which serves the South Bank and Bankside - from six buses an hour to just three.
From Saturday 10 February bus route RV1 – from Covent Garden to Tower Hill via Waterloo, the South Bank, Bankside and London Bridge – will operate every 20 minutes.
TfL says it is making the change "to match demand" for the service.
The RV1 was introduced in 2002 with a 10-minute frequency.
Hydrogen-powered buses are used on the route which is operated by Tower Transit.
Since September 2016 the RV1 has been operating to a 'temporary' timetable – with buses every 12 minutes – due to the long-term diversions at both Waterloo and London Bridge.
Faced with a budget squeeze, TfL has been cutting frequencies on bus routes across London but few have seen such a drastic reduction as the RV1.