Dangerous chemicals could not be stopped from coming out of an incinerator, an engineering expert told a public inquiry.

University of Sussex professor Chris Chatwin said the amount of pollution could not be monitored accurately and existing safety limits were inadequate.

He told the inquiry examining council waste plans the dangers from chemicals, such as dioxins and furans, and tiny particles are poorly understood.

He said: "There is always toxic material coming out of incinerators and frankly there always will be. It is not possible to stop it."

Prof Chatwin, giving evidence for pressure group Defenders of the Ouse Valley and Estuary, said a burner of the size proposed at Newhaven would emit about 133,000 tonnes of toxic gases every year.

He said the emissions would include dioxins, furans and ultra-fine particles, many of which could not be trapped by filters. The most dangerous substances are likely to escape in bursts and not be detected by monitoring equipment.

Many of the chemicals have been linked to increased rates of cancer, and the World Health Organisation believes dioxins levels in particular should be reduced.

Prof Chatwin said: "The source of dioxins is from industrial processes and incinerators, and incineration is a major source of dioxins.

"The last thing we should be doing is building incinerators, which will increase the level of dioxins in the environment.

"It is clear to me the production of dioxins in incinerators is not well understood."

The Brighton and Hove City Council and East Sussex County Council waste plans propose incinerator sites at North Quay, Newhaven, and Mountfield Mine, near Robertsbridge.

The two authorities have already signed a waste disposal deal with contract Onyx Aurora, which wants to build a single burner at Newhaven.

Timothy Howard, representing the councils, said incinerators had to comply with EU rules and monitor dioxins and furans. Monitoring does not have to be continuous.

A burner would have to win planning permission and a pollution control licence from the Environment Agency.

The councils intend to put detailed evidence on pollution claims to the inquiry in the autumn.