The music blog 5:4 reveals, this turned out to be a setting of words from Richard Jefferies' spiritual autobiography "The Story of My Heart". The Proms programme does not reveal what those words, were but 5:4 thinks he knows:
Here this moment, by this tumulus, on earth, now; I exist in it. The years, the centuries, the cycles are absolutely nothing; it is only a moment since this tumulus was raised; in a thousand years it will still be only a moment. To the soul there is no past and no future; all is and will be ever, in now.