Bath's Liberal Democrat MP Don Foster has issued a damning public statement indicating his unease with the project, which features a metal, glass and brick round tower - dubbed the 'busometer' (Fresh opposition to Wilkinson Eyre Bath scheme).
He said: 'I have no problem with good modern design sitting alongside our heritage architecture, but something has obviously gone disastrously wrong in this case.'
More than 10,000 residents have signed a petition opposing the multimillion-pound terminal and accompanying retail and housing.
Crucially, the interchange involves bulldozing local landmark Churchill House - a 1920s former electricity company headquarters designed by WA Williams (pictured). It also means the loss of a ramp created by Isambard Kingdom Brunel.
Ian Thorn, chairman of Bath Liberal Democrats, said 'Almost everyone I've talked to about the design - feels that it is unsightly and inappropriate for a World Heritage City - and I agree with them.'
Wilkinson Eyre is being pressed to redesign the tower using stone cladding rather than metal, but Southgate developer Multi Development has said it will push ahead with the original plans.
Bath and North East Somerset Council leader Paul Crossley has praised Multi for its efforts to have Churchill House dismantled for future rebuilding rather than be demolished.
Crossley was part of the planning committee which originally passed the scheme four years ago. But he too has expressed reservations about Wilkinson Eyre's design and has asked Multi to consider modifying it.
He said: 'If the new building can be modified to address some of the design concerns that would be welcome, but this is not a U-turn. I expressed a dislike for the design but it was a unanimous decision to pass this scheme.'
He added: 'What I have asked is if the developers can look again at the design - but I have no authority to make them do this.'
Wilkinson Eyre declined to comment.