A crucial environmental report was produced too late to influence controversial council waste plans, a public inquiry was told.
Waste policy expert Alan Potter said the Best Practicable Environmental Option (BPEO) report was only finished after a proposal to build an incinerator had been fixed.
He said: "Clearly the timing means the strategy that underlines the plans is not informed by the BPEO approach.
"The production of the BPEO was well after the strategy was developed."
Brighton and Hove City Council and East Sussex County Council published the report more than four years after they started work on the waste plans and after two statutory consultation exercises.
An environmental study has to be produced for all major developments, such as the incinerator proposed at North Quay, Newhaven.
Mr Potter, giving evidence for Lewes District Council, said a planning inspector examining proposals in Hull criticised a BPEO in similar circumstances, saying the evidence appeared "geared towards the defence of decisions already made".
He said the report was biased towards incineration and had not studied alternative technologies, which could be adopted instead of burners.
Campaigners have already claimed the BPEO backed the option proposed by contractor Onyx Aurora from nine alternatives.
The inquiry is examining waste plans that identify North Quay and Mountfield Mine, near Robertsbridge, as potential burner sites.
Onyx Aurora, which has signed a £1 billion waste disposal contract with the city council and the county council, proposes a single burner at North Quay.
Mr Potter said there was "substantial concern" about disposing of toxic fly ash produced by burning waste.
An incinerator of the size proposed at Newhaven is expected to produce about 5,000 tonnes of fly ash a year.
The BPEO, backed by the two councils, relies on a costly policy of exporting fly ash to sites outside the area.
The authorities said the BPEO was not biased and had been produced in accordance with Government guidelines.
The inquiry is expected to continue until the autumn.
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