Sir Terry Farrell has warned that Boris Johnson’s proposed airport in the Thames Gateway could be “a complete disaster”.

But he added that Johnson’s plan was evidence of fresh thinking on the question of what to do with the area.

The London mayor has proposed the construction of an “eco-airport” on the Isle of Sheppey in Kent, to be built instead of a third runway at Heathrow.

Farrell, the Thames Gateway design champion, said: “I respect Boris for looking at different ideas, but it is utterly unproven that it could work. It could be a complete disaster, or a total success, I don’t know. But if you don’t ask questions, you don’t get answers.” He added that the idea of an eco-airport was a “contradiction in terms”.

Farrell made the comments ahead of the official unveiling of his Thames Gateway Parklands plan, due to be launched on Thursday by Margaret Beckett, the new housing minister.

The architect said the masterplan, which was drawn up over the past year in collaboration with various stakeholder groups, was “a holistic rethinking of an eco-region”.

The government has pledged to invest £35m in Farrell’s scheme.