Signs of a revolt by councillors against a proposed local authority merger came to the fore at a public meeting as the two councils' cabinets overwhelmingly backed plans to look into a business case for the move.

Waveney District Council leader Colin Law and his Suffolk Coastal District Council counterpart Ray Herring, along with members of their cabinets, argued strongly in favour of creating a 'super-council', which would be the largest district authority by population in the country.

At a joint meeting of their two councils' cabinets at Lowestoft's Riverside building last night, they said the merger 'will bring significant improvements in service delivery' by saving more than £800,000 per year across the two councils.

However Sonia Barker, the Labour opposition group leader for Waveney, asked: 'How is local democracy going to be best served by having decisions about Beccles and Bungay made by someone from Felixstowe?'

And in what was an otherwise unanimous vote by both council cabinets to go forward to the next stage of letting officers build a business case for the merger, Andy Smith – portfolio holder for economic development and coastal management at Suffolk Coastal – spoke out against the plan.

Abstaining from the vote, he asked: 'Would there not be a democratic deficit?

'It is inevitable that members will have half the influence on a larger council than a smaller one.'

Suffolk Coastal portfolio holder Richard Kerry said that while he was a business plan being produced: 'The people we've got to convince are the taxpayers.'

Green councillor Graham Elliott, who represents the Beccles North ward, added: 'I'm not desperately against, but as long as we have some democratic accountability.'

A local advisory referendum would be held in June or July this year to gauge people's views, but it is not legally binding in the same way as the EU referendum.

Briefing councillors ahead of the meeting Arthur Charvonia – strategic director at both councils – said a merger could be a 'natural extension' of the councils' current partnership.

Waveney and Suffolk Coastal have shared a chief executive since 2008 and a senior management team since 2010. Most staff work across the two councils except where there is a need for separate services, such as when they currently administer two sets of elections for each council.