He is the renowned architect who is Mayor of London Boris Johnson's design adviser.

But leading planner Sir Terry Farrell has spoken out against plans for a multi billion pound Thames Estuary airport.

The Kent-based designer, pictured right, slammed the proposals today as he argued the case for a railway hub in west London linking five airports by high-speed rail.

Mr Johnson is backing plans to build four floating runways in a £70 billion project - dubbed Boris Island - off the north Kent coast.

Meanwhile, architect Lord Foster revealed plans in August for the world's biggest airport on the Isle of Grain.

His four-runway project would cost an estimated £50 billion, handle 150 million passengers a year - twice the number of Heathrow - and be powered by 1,000 submerged generators.

However, Sir Terry - who is Mr Johnson's design adviser for a 50-mile stretch along the River Thames - said his proposal is a "significantly more cost-effective and sustainable alternative".

In a speech in west London, he promoted plans for a railway depot called Old Oak Common between London's Harlesden and Acton.

Sir Terry said: "Heathrow will be just 11 minutes away and four other airports - Birmingham, Luton, Stansted and City Airport - will be within half-an-hour.

"We need to adopt the latest thinking on air-side rail travel to make sure the previously complex logistical and baggage transfer issues are no longer a barrier.

"It is by far the most cost-effective and sustainable solution for air travel. If we build a brand new £50 billion airport to meet today's demands, then what will we do after 20 years of exponential growth. Build another one?"

Sir Terry, who lives in Rolvenden, near Tenterden, is best known for designing London's MI6 building and last year wrote Kent County Council's aspirational 21st Century Kent document.

Medway Council has run a joint campaign since 2009 with Kent County Council against a proposed Thames Estuary airport.

Leader Cllr Rodney Chambers said: "I welcome the view of such a renowned architect as Sir Terry Farrell that the Thames Estuary airport is a non-starter.

"We would urge the Mayor of London to listen to the views of all - including his own adviser - and realise that the overwhelming consensus is against his airport plan, which is not needed, will cause serious damage to the environment and could cost up to £70billion."

Last week, an ICM poll revealed more than three-quarters of Britons do not support a Thames Estuary airport.