A "secret" council-commissioned report shows a new Greenwich river crossing would increase congestion, campaigners say - as their survey shows already frightening levels of pollution in the area.

The report, obtained by No to Silvertown Tunnel campaigner Darryl Chamberlain, was commissioned by Greenwich Council back in 2012 to look at the potential for a DLR extension to Eltham.

But it also points out weaknesses in plans for a new tunnel connecting the Greenwich peninsula and Silvertown near the current crossing at Blackwall - a project the council is backing, along with Mayor of London Boris Johnson.

Greenwich Council says the DLR report has now been superseded by the Silvertown plans and was never intended as a proper study of the peninsula link.

But the report warns a link would encourage more traffic to the peninsula, stating: "The likely outcome would be the exhaustion of the Silvertown Link capacity within a relatively short timeframe with exacerbated congestion on the local road network.

"This could only be mitigated by a new high quality public transport link, such as a DLR extension."

Campaigners have seized on the report as evidence that a new crossing would only increase congestion, not ease it.

It comes after recently-published research by No to Silvertown Tunnel and the Don’t Dump on Deptford’s Heart group - fighting plans for work on Thames Water's 'super sewer' in SE8 - showed air pollution levels as much as two-and-a-half times over European legal limits.

Obtained by monitoring 150 sites across south east London for nitrogen dioxide, the research showed "dangerous" levels of the pollutant at the New Cross one-way system, Lee High Road, Charlton's Bramshot Avenue underpass and at roads across the area.

Mr Chamberlain said: "Local politicians are backing dangerous plans for the Silvertown Tunnel rather than taking a stand against the lethal air pollution that blights our communities, and the traffic that causes it. A new tunnel will only bring extra traffic - it won't bring relief from congestion or pollution.

"Generations of local people have paid the price for their lack of investment in new public transport, walking and cycling facilities, while politicians prioritise the profits of property developers over people."

A spokeswoman for Greenwich Council said: "This internal report specifically looked into the feasibility of extending the DLR to Eltham. The report focused on whether a route could be identified from the Peninsula to Eltham and was not intended to examine any relationship with the proposed crossing. This work was commissioned before the Mayor of London commenced his feasibility study for the proposed Silvertown Tunnel.

"The council's position has been consistent that all studies relating to the economic and environmental impact of river crossings, including the inclusion of public transport access which we support, should be undertaken by the project promoter which is Transport for London, under the auspices of the Mayor.

"It makes sense for this work to be undertaken first before any decision to commission further work within the borough."

To see the pollution study results visit silvertowntunnel.co.uk