Waverley Borough Council's leader has denounced a county council proposal to create the largest unitary authority in England as "a disaster" and "a power grab by Surrey that should be resisted at all costs".

Surrey's 1.2 million population means it would overtake Birmingham – population 1.14 million – as the sole principal local authority serving the greatest number of people.

It would be twice the size of the next biggest unitary, Cornwall, prompting worries that councillors would be too remote from the people they serve.

Waverley council leader John Ward, of Farnham Residents, said: "It is far too big, it would be a disaster. It's totally and utterly unrealistic – a power grab by Surrey that should be resisted at all costs.

"Smaller ones would be closer to the people, more responsive to their needs and more familiar with what's going on."

Surrey Leaders' Group – the council leaders of all 11 boroughs and districts – agree that two or three unitaries would be better.

The collaboration thinks three unitaries could each have 80 councillors representing 400,000 people – that is about one councillor per 5,000 people.

One option for a single unitary, of 162 councillors, would mean one councillor per 7,400 people.

Group chairman Nick Prescot said they were keen for residents to have a say in where boundaries might fall.

One common suggestion was to have Surrey Heath, Runnymede, Spelthorne and Elmbridge as one council area in the north of the county; Woking together with Guildford and Waverley; and a third council made up of Mole Valley, Epsom and Ewell, Reigate and Banstead and Tandridge.

Woking borough councillor Ann-Marie Barker thought Woking could, on the other hand, fit well with areas such as Guildford, Waverley and Surrey Heath.

Surrey County Council leader Tim Oliver said: "This is not about any one authority getting more power. This is about how we deliver the statutory services that local government has to deliver, and how to do that with real local engagement."

He said he did not understand the need to break up the county into a number of smaller areas – and said this would not save as much money.

He said: "The county council already delivers all children's services and all adult services to 1.2 million residents so actually, in some respects, all this would be doing is adding on some of those responsibilities that sit with the districts and boroughs, so it's not as if we're not already looking after 1.2 million residents - we are."

He added: "What the government has seen is that small unitaries don't really produce those greater efficiencies."

Mr Oliver is in conversation with Boris Johnson's government about abolishing the 11 district and borough councils in favour of a single unitary authority.

While many within those lower tier councils have voiced their disapproval of the idea of one huge council running everything, Cllr Oliver said it could save a lot of public money.

He said: "By not having 12 chief executives, 12 finance directors and so on that would generate a saving in excess of £30 million every year, which is the equivalent of about 4% on the council tax, so it's a sizeable number."