It's a great site - I went there over ten years back now, and it was highly memorable.
Speaking as someone who has been involved in negotiating access to a couple of well-preserved underground sites in Surrey, and with conditions imposed by two separate owners, I can say that patience bears rewards. The sites I mention were denied to anyone for about 15 years, and by gentle persuasion that mine explorers are pretty harmless individuals, and take responsibility seriously, access has been possible for over 20 years now.