Kelly's message follows the publication of the new Thames Gateway Interim Plan, which set out proposals for 160,000 family homes and more green spaces throughout the region - but not a national park as suggested by Farrell.
The statement came at the opening of the annual Thames Gateway Forum, and in a later speech the new Thames Gateway chief executive Judith Armitt claimed a 'national park like Farrell's would restrict development.'
Farrell's original proposals looked at a deliberately designed 'Thames national park' reaching right through the heart of London to the limit of the tide at Teddington.
The masterplan looked at a 'rural renaissance', which called for 90 per cent of the Thames Gateway's proposed developments to be built within the M25, leaving more than 85 per cent of the national park area unbuilt on.
Despite this latest blow, Farrell welcomed the news of the provision of more housing, but warned the scheme needed more detailed plans.
'I think it's a big step forward, especially by looking at the Thames Estuary as a whole,' he said. 'But the parklands are not quite joined up enough, and they don't seem to have specific proposals as yet.'