A political row has broken out over Norfolk County Council's handling of taxpayers' money in paying contractors.
County Hall's leader David Bick claims millions of pounds were wasted because of a lack of oversight by his Conservative predecessors.
Reform leader Mr Bick accused the former Tory administration of being "lazy, lethargic, incompetent and, at times, negligent" over the way contracts using taxpayers' money were managed.
The county council spends more than £900m every year on contracts, including one-off major projects such as the revamp of Norwich Castle and for contractors to provide services, such as social care, highways work and home to school transport for children.
Mr Bick, who became the council's leader after May's elections, said his administration had uncovered numerous examples of overspends on contracts and claimed more were coming to light.
He said: "This council has wasted tens and tens and tens of millions of pounds. And it was done because, and this is no reflection on officers, because it was an inadequacy of process at the time.
"The political oversight was lazy, lethargic, incompetent and, at times, negligent".
But Kay Mason Billig, leader of the Conservative group and the former leader of the council, hit back.
She said: "What we should not do is rewrite history by assuming that every project which exceeded its original budget did so because of avoidable failures by the previous administration. That is simply untrue and just political rhetoric.
"Anyone who has been involved in major capital projects knows that costs can change because of inflation, unforeseen site conditions, changes in scope, supply chain pressures and circumstances entirely outside the council's control.
"Sometimes there will be lessons about project management too, but those should be established by evidence, not assertion."
Reform leaders said, since they took control of County Hall in May, they have introduced new measures to provide better oversight of contracts.
But Mrs Mason Billig said: "Procurement, contract management, risk assessment and financial controls existed before May.
"We support rigorous scrutiny of major contracts. But that scrutiny should apply equally to the claims being made about them."
In June, it was revealed the bill for the revamp of Norwich Castle's keep had increased to £34m.
When work first started on the award-winning Royal Palace Reborn project in 2020, it was estimated it would cost £13.5m.
But the scheme was hit by delays due to the Covid pandemic, while the war in Ukraine was blamed for problems in securing steel.
Inflationary costs for materials and labour meant the bill for the scheme, which included contracts with builders Morgan Sindall, rose.
Just under £13m of the cost came from National Lottery Heritage Fund money, but the county council has put in £18.5m.
Officials said the need to make changes to the project after new features were uncovered during work on the Grade I-listed building also pushed up costs.
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