So come on English Heritage, we are after all paying your wages......tell us why it was necessary to cut a new trench into the heart of Silbury..

'Is there anybody there?' said the Traveller,
Knocking on the moonlit door;
And his horse in the silence champed the grasses
Of the forest's ferny floor:
And a bird flew up out of the turret,
Above the Traveller's head
And he smote upon the door again a second time;
'Is there anybody there?' he said.
But no one descended to the Traveller;
No head from the leaf-fringed sill
Leaned over and looked into his grey eyes,
Where he stood perplexed and still.
But only a host of phantom listeners
That dwelt in the lone house then
Stood listening in the quiet of the moonlight
To that voice from the world of men.

Its not for us to know Littlestone. Think of it as one of a growing list of wewon'tbutactuallywewills. In this instance it qualifies by virtue of the previous constant assurances that "we won't be building a bigger tunnel" whereas a large trench constructed in the floor of the existing tunnel and stretching the full distance from the centre to the outside will produce, indisputably, a larger tunnel.