The two areas of contention are a 1920s former electricity company headquarters and a ramp designed by Isambard Kingdom Brunel, which Bath Council and Network Rail wish to demolish.
The building, Churchill House ( pictured), was designed in 1928 by W A Williams, who attempted to create a 'temple of electricity', which would showcase electricity to the public.
Campaigner and Bath councillor Bryan Chalker, said: 'It's a wonderful building, marrying Classical and Art Deco design. The council is trying to replace it with a glass tower eyesore.
'They do not need to knock the building down to build the interchange. We have been dealing with these people for two years and they are simply entrenched with their ideas, and refuse to compromise.'
He added: 'Bath is in danger of losing its world heritage status with these types of buildings.'
The developer says it is exasperated by protestors, who are already disrupting the work.
David Redgewell, regional director of quango Transport 2000, said: 'Surveyors have to survey the site at night to avoid disruption from protestors. The redevelopment has to be done.
'Bath Spa is one of the major transport links in the South West, and requires a complete overhaul. It needs a new bus station and the train station needs to be expanded. There is no disabled access, so it is not fit for requirements. It's impossible to save the building.'