No-one could deny the tunnel would pay a welcome knowledge dividend for Prof Bell and the rest of us. But the issue, plain and simple is - at what cost? By EH's own account, it's vast in terms of losses that wouldn't be sustained otherwise.

In conservation terms, Littlestone, is there a precedent for this sort of thing? Can anyone unilaterally designate a cubic foot of Silbury 1 as being worth the sacrifice of 45 cubic feet of Silbury 2? That's the mooted rate of exchange that the tunnel is said to involve. Equally, if EH has a statutory duty to learn and a statutory duty to preserve, whence their power to rule in favour of learning even when it involves flouting their duty to preserve? Where's the authority?

My inclination would be to say thank you but no thank you - on the figures so far supplied your plan stinks. You're welcome, after five years of very limited disclosure, to offer the public every shred of data and to try to persuade them, but I think they might say "the Bells can do their studying but it'll have to be the Bell great great grandchildren, as at present we'd prefer to avoid huge damage to our monument."