Can you post an image of the attached plan?
"We have also purchased the mining report last week, upon hearing this news, to see what is mentioned, it states.....
Mine entries
Within, or within 20 metres of, the boundary of the property there are 2 mine entries, the
approximate positions of which are shown on the attached plan."
I have never seen a coal board search. What I have seen are many non-coal searches. Some of them are downright appalling. One of the largest GIS data portals offers a range of search services relating to it's incredible database. Sadly, the mining information has been entered in the most incoherent way, to the point that it's conclusions are at best nebulous and at worst misleading. However, they are probably insured, like everyone else.
What happens in the world of non-coal is that it's basically insurance brokering.
Lenders don't take risks. Banks take pretty much zero risk with their lending. If they do take a risk, it's backed up by someone's PI insurance. So, you do the box ticking exercise and there are 2 potential outcomes. Pass and Fail.
If it's a pass, all is well. (if your house starts to collapse, there will hellup in the form of conveyancerssearch wholesalersearch seller and who neglected to do their job properly).
For workings which are deemed to designate the property a fail, the conveyancer/agent usually recommends a physical investigation to be done. Usually with a drill rig. Cue big drill showing up with a load of pasty powered hillbillies and someone important sat in a deckchair drill a load of different holes to try and pierce the structure. Following a couple of days of noise, floods of inorganic pancake mix and general mess, a report is produced.....this stays attached to the property and is permanent....unlike a mine search.
This report either says "pass" (nothing found) or "fail" and details the problem. The problem itself then informs a structural engineer what solution needs to be employed. At this stage, you have probably got yourself serious expense. (read your insurance small print very very carefully). In fact, read all the small print on any search document and raise an eyebrow.
The upshot of my point is that a desktop search which has turned up a problem is the first step in a process to assess the risk of workings to a property. The next step is probably in the order of £3k for some drilling contractors and a geo to come out and test the place. In the grand scheme of things, this is cheap for what it is and you have a piece of paper to say "my house is OK" rather than anyone else, who has a piece of paper which says "This house is free from mine workings to the degree that is considered an acceptable asset for lending to occur against*"
*Footnote:- Whilst we have busted a bollok to insure there are no workings according to pawing through our huge archive of plans, maps, heresay and previous site investigations, it's quite possible that there are unrecorded workings pretty much anywhere and if your house falls into one of these.....mmmmm sorrry. LOL !!!"
I suppose that the first thing someone would do in this instance is get a second opinion. That would ascertain if the search seller had done their work properly.
Either way, I would expect that a problematic search could be a rarity which some agents/solicitors would find a novelty and be unaware of the next stage in the process. It isn't a case of "my house is now unsaleable" it's merely a drill-it problem. For coal workings, a larger firm in an area of more coal workings will provide information as to what is the next stage for your particular area.
Anyway, we weren't here to talk about mining searches!
Whilst we are here talking about interesting and interactive data, BGS also have a very good mapping "gubbins", there is also borehole data which is worth a look. This includes some coal measures info.