LONDON, Aug 13 (Reuters) - Prince Charles said the widespread use of genetically modified crops would the "biggest disaster environmentally of all time" in a newspaper interview published on Wednesday.

The 59-year-old heir to the throne is well known for his support of organic farming but his comments during an interview with the Daily Telegraph are his most outspoken attack yet on GMO foods.

His views will strike a chord in Britain where biotech crops have faced significant opposition, with concerns centred on both food safety and possible environmental impacts.

Small farmers would be the victims if "gigantic corporations" took over the mass production of food.

"We (will) end up with millions of small farmers all over the world being driven off their land into unsustainable, unmanageable, degraded and dysfunctional conurbations of unmentionable awfulness," he declared.

He said "excessive approaches to modern forms of agriculture" had already damaged water supplies in India's Punjab and in Western Australia.

"What we should be talking about is food security, not food production -- that is what matters and that is what people will not understand.

"And if they think it's somehow going to work because they are going to have one form of clever genetic engineering after another, then again count me out, because that will be guaranteed to cause the biggest disaster environmentally of all time."

His intervention comes as a wave of food inflation has reopened the debate on the ways science can boost agricultural production.

Earlier this year Britain's chief scientist John Beddington said GMO crops should not be shunned as agriculture seeks to respond to rising food demand, particularly from China and India, at a time when climate change is expected to hit yields.