A cross-section of Lord Foster's plans for a new Thames Estuary airport

Protesters are set to descend on London's City Hall today to campaign against a proposed airport in the Thames Estuary.

The groups, including representatives in Kent, are opposed to plans to build an enormous hub airport off Kent.

Originally mooted by London Mayor Boris Johnson, Boris Island was said to be a 20-year project costing anything up to £70billion.

Then, in November last year, world-renowned architect Lord Foster unveiled a more ambitious project on the Hoo Peninsula.

If built, it would more than double the capacity of Heathrow, handling up to 150 million passengers each year, 24 hours every day. It would have four runways, each 4km long.

But both projects have attracted huge criticism, including attacks from Medway Council, which claims the project is unviable, expensive and an environmental hazard.

Now demonstrators are set to gather at City Hall - just one day after Mr Johnson said he was committed to pushing through the scheme.

They claim the Mayor has championed the scheme in the face of opposition from local politicians and environmental campaigners and despite the Estuary being beyond London’s borders.

A section of the Thames Estuary airport. Designed by Lord Foster

Campaigners from No Estuary Airport, the Campaign against Climate Change and AirportWatch will be joined at their protest by London Assembly members Jenny Jones, Caroline Pidgeon and Murad Qureshi.

Phil Thornhill from the Campaign against Climate Change said: “There is at the moment no way of sustaining air travel on a large scale without precipitating a potentially catastrophically high level of climate destabilising emissions which will wreck the future for everyone.

“Boris Island is not the answer. We need to think more deeply and imaginatively on how we organise transport systems for the future that are truly sustainable.”