The best summary I can give is that services crossing the City will go around it instead, and services that end in or near the City will tend to stop at a major junction near the boundary of the closed area. No bus services are cancelled, but most of them will suffer from uncertain timetables and offer a slightly jumbled service.

This map of bus routes may help to give an overview. It’s not quite complete, being based on the TfL map of buses through Bank, but it includes all the main cross-city routes and shows their diversions and interruptions.

To and from the east

Every bus stop between Trafalgar Square and Liverpool Street is closed. Most buses are going round the closed area, e.g. the 26 to
Hackney will go south of the river and then cross London bridge to pick up its normal route near Liverpool Street, and the 8, 15 and 25 (Bethnal Green, Mile End, Poplar) will get to Holborn Viaduct and then detour north before picking up their routes on the other side of the City. A few services will just turn round at Liverpool Street, including the 242 and 388 from Hackney.

To and from the north

There is a similar situation for buses from the north and north east. They will travel south as usual until they get to Clerkenwell Road or Old Street and then in most cases they are diverted around the edge of the closed area. For example, the 76 and 341 from Dalston and Islington will detour along Old Street and Holborn to get to Aldwych and pick up their usual route. Services heading straight into the city will tend to stop at the northern boundary: the 46 from Camden and the 17 from Holloway can only get as far as Holborn Circus.

To and from the south

From the south your main concern is the closed bridges. Blackfriars bridge is completely closed and Southwark Bridge doesn’t connect to much. Services are mostly diverted rather than truncated, e.g. the 139 will get through to Waterloo but without the usual loop around Aldwych, and the 45 from St Pancras to Brixton will go round to Waterloo bridge instead of through the City.

Please note that southbound disruptions, though minor, will last longer than most because Blackfriars bridge remains closed in the evening for the fireworks display.

To and from the west

You shouldn’t be affected much. Buses starting at Trafalgar Square and heading west will run as usual and Victoria services are unaffected. Services that start in the west and cross the centre, e.g. the 11 from Fulham to Liverpool Street, will tend to stop and turn around at Trafalgar Square.