Council leaders have been urged to drop plans for a tunnelled Bristol underground in a key vote on Friday which will decide the future of the project.

The West of England Combined Authority (WECA) committee will vote on October 6 on progressing its "Future4West" plans, for a mass transit system centred around Bristol, to the next stage — an outline business case. But the possibility of a tunnelled "tube" underground could be dropped from the plans, in favour of mainly overground options with short sections of cheaper "cut and cover" underground.

The transport chiefs behind a new report about the scheme recommended progressing the plans and considering all transport options, warning if WECA excluded options at this stage they could find themselves "ultimately failing to deliver what may ultimately prove to be the most beneficial scheme" — or facing a legal challenge from businesses impacted by the roadworks involved in the overground and cut-and-cover options.

But at a meeting of WECA's scrutiny committee on October 2, which reviewed the report, some Bristol councillors called for the committee on Friday to only progress the case for the cut-and-cover and overground routes.

Hengrove and Whitchurch Park councillor Tim Kent — who commented that the proposed routes would not serve his area — warned that the city getting the estimated £15-18bn needed to build a system with tunnelled routes was "fantasy." He said: "I understand that the officers have said at the moment everything should be left on the table. I don't think any more money should be wasted on looking at the four tunnelling routes."

He highlighted that the report stated that tunnelled routes would offer a benefit cost ratio of 0.1 — meaning that they will deliver a public benefit of 10p for every pound spent.

Cllr Kent said: "I think what we need to do is we need to be ambitious but realistic. There's no point setting an ambition which actually will stop other public transport improvements from occurring. Because if this is our big thing and that's what we are trying to fund, we won't be funding other measures we could be doing in the short to medium term."

His views were echoed by Clifton councillor Katy Grant, who warned there was an "opportunity cost" to spending more time on the "unimaginably expensive" tunnelled underground plans. She said: "I just want to remind us to juxtapose it with the howl of anguish we heard earlier from the public around the very different and very immediate set of things they want."

At the start of the meeting, members of the public had spoken at the scrutiny committee and urged the combined authority to reinstate axed buses and look at ways to fix the bus service such as franchising. Francis Bennett, a doctor in St George, told the committee that people dependent on buses were "missing doctors' appointments, getting fired from work for being continually late, spending hours a day waiting for buses that don't come."

At the WECA committee on Friday, Metro Mayor Dan Norris and the leaders of the three councils which made up the combined authority — Bristol Mayor Marvin Rees, South Gloucestershire council leader Claire Young, and Bath and North East Somerset Council leader Kevin Guy — will vote on progressing the business case and whether the tunnelled routes should remain a part of the plan.

Mr Norris will have a veto in the vote. In February, before his transport chiefs had drawn up this report, he was asked on BBC Points West to sum up if Bristol would ever get an underground in one word. He said: "No."

In a post on his blog last week, Bristol Mayor Marvin Rees reiterated his view that an underground-overground hybrid solution is the only viable option, without causing 'chaos' on the existing road network above ground.

He wrote: "We must go underground in the densest areas or else we cannot deliver a segregated, reliable, fast transport system that people will use in big numbers. Do not be fooled by the argument that it's too expensive."