Another forum member whom to contact as well as Iclok would be LeeW, who is another very knowledgeable AN contributor about the coalmining area that you are asking about.
Incidently your conveyancing solicitor should have done a search on your property to see what lay beneath the property you were proposing to buy before you exchanged and completed contracts. For example I purchased a cottage in Bonsall back in 2003 and although I knew approximately where workings (ie. old lead mines and open cast fluorspar workings) were in the area, the detailed report about the area that was produced suprised me and threw up a lot of information that I wasn't aware of. There are lots of firms around the area who specialise in supplying these type of reports to solicitors. Has your solicitor not shewn you such a report? Just curious.