The seven, led by the Government's wildlife conservation arm, English Nature, say these trees are misunderstood. They may look as if they are dying but they have a special place in the country's history and culture. They are also invaluable to lichens, insects, fungi and birds.
The trees are 500 years old or more, and a few may have lasted longer than a millennium. Often their heartwood has rotted away, leaving a cavern inside their great girths and "staghorn" bows, which have been dead for decades, projecting into the sky above the living branches.
The rot holes and hollows provide shelter and nesting places for bats, woodpeckers, tits and fly-catchers. Hundreds of insect and spider species depend entirely on the large quantities of dead wood found in such veterans.
Foresters normally fell a broadleaf tree within 200 years of the start of its life, because after that the quantity and quality of its usable timber declines. The few found dotted round the country have escaped for one reason or another.
Today they remain threatened, sometimes because they are regarded as senile and ugly and sometimes because land owners fear huge pieces of wood breaking off.
Through the Veteran Trees Initiative, the seven organisations want to give people advice on how such trees can be made safe. They also want to build up records of where the veterans are found.
The initiative is being launched in Windsor Great Park, Berkshire. The choice is apt because the Duke of Edinburgh provoked much anguish and criticism last year when many veteran oaks lining an avenue in the park were felled precisely because they had become old and twisted.