Manchester City Council has passed a motion requiring affordable housing viability assessments to be published, as concern about housing in the city centre grows ahead of local elections in May.

The motion, proposed by Labour backbenchers, also requires commercially sensitive information to be made available to members of the council's planning committee.

A recent controversial study of 79 new developments concluded both Salford and Manchester were underproviding affordable housing in the city centre. That was a result of viability assessments suggesting schemes would not work if 20% affordable housing was required, the report said.

Salford council collected £4.9M in lieu of providing affordable housing, whilst Manchester collected £856K. The figures are disputed by Manchester City Council.

"This motion signals a new direction in council policy in this area," the motion's seconder, Labour councillor Garry Bridges said. "The secrecy surrounding these assesments undermines public confidence in their rigour.

"There is widespread suspicion that developers can use these assessment to avoid their responsibilities. We need to be more robust with developers about their obligations."

Bridges asked for consultation on what viability assessments should contain. Supporting the motion, Labour councillor Angelika Stogia said even "if they had to unpick the planning process start to finish" the council's executive would come back with reform proposals later in the year.

Although he supported the motion, the council's sole opposition member — Liberal Democrat former MP John Leech — cast doubt on the motives.

"The timing of this motion shows the electioneering motive behind it," he said. "Your policy of taking developers' money [paid in lieu of affordable housing in the city centre] and spending it in the more affordable parts of the city is creating social cleansing of the less well-off in the city centre."

Council leader Richard Leese, conceding that the motion would pass, called the suggestion of social cleansing in the city centre obscene, saying it was based on no data and completely made up.

The council executive will prepare new proposals to implement the motion in June.

A webcast of the meeting is available here.