The academy trust behind a new science and maths Free School is refusing to give up on hopes of moving into Norwich's historic former fire station in September – despite the proposals still not getting planning approval.

The Sir Isaac Newton Sixth Form is due to open in just three-and-a-half months' time. But last night, talks over whether to grant planning permission to convert the Grade II listed Bethel Street building reached a stalemate after Norwich city councillors defeated a motion to reject the plan – as well as a motion to approve the proposals.

The application has now been deferred to the committee's next meeting when it is hoped a new set of councillors will have more luck coming to a decision.

The Inspiration Trust, led by chief executive Rachel de Souza, said it was disappointed by councillors' failure to reach a conclusion.

But while admitting there was a possibility the fire station would not be ready in time for students arriving in September, Mrs de Souza said: 'I'm an optimist.

'It will be great if we can. If we have to use our back-up plan, we will do that. The point is the school is going to open in September.'

The Inspiration Trust has still not revealed what its 'plan B' is for students who have applied to begin their A-level studies at the Sir Isaac Newton Sixth Form this September.

Mrs de Souza said her team was still 'dotting the Is and crossing the Ts' but would be making an announcement 'very shortly'.

The Sir Isaac Newton Sixth Form Free School proposals were approved by education ministers last year.

While intending to retain key features including the firemen's poles, billiards board, ornate handrails in the stairwell and the large wooden doors at the front of the building, the plans include a large lecture theatre, state-of-the-art laboratories, a cafe, and a new tower.

Addressing the planning committee, Mark Evans, who will be principal of the free school, said: 'The fire station, to me, instills such passion. In my view, it's perfect. It's the most impressive building for a school I've ever seen. I go in there motivated and enthused.'

But a number of councillors voiced concerns about the application which ranged from worries about the volume of traffic which would be created by a school to the impact on the listed Bethel Street building.

They also questioned the need for a sixth form in the city centre, suggesting there were sufficient school places elsewhere in Norwich and Norfolk and approving the free school plans would impact on the sustainability of other local communities.

Councillor Stephen Little said: 'I hate what's going down here. I hate the impact it could have on other schools.'

Mike Stonard led the attempt to turn down the application on the grounds that it was 'contrary to current and emerging policy', a lack of confidence in the travel plan – where the site would be a 'no car zone' and students would be encouraged to walk and cycle – and that there was already sufficient choice for pupils.

Councillors were warned a decision to turn down the application was unlikely to stand up against any appeal.

Planning officers said national policy included a 'presumption in favour' of free school bids and that the government's approval of the school suggested any questions over the need for the school had already been determined.

Committee members were also warned a planning inspector who suspected the decision had been made for political reasons could award costs against the council. They were advised to include concerns over the impact on the listed building and a preference for homes on the site with any decision to reject the plans.

Paul Kendrick led the failed motion to approve the plans.