Look, when it comes to "religious" beliefs people seem to belief what ever they like with out recourse to evidence.

One point:

"Even today, we have the mythology of "well witching" that actually seems to work to find water sources with a forked branch."

No it doesn't work - it's as simple as that.

People also pull in Celts fairly randomly - the historical world is not at all sure who they were or what what they specifically did so the idea of 'Celtic' influence in Derbyshire is on very shaky ground.

If the fall back is well - all things are possible then fine believe what ever you like - but don't expect to be taken seriously.

The website you give a link to Joe is interesting but I wonder how historically sound it is:

"The Celts were tribal warriors who loved to fight with death holding no fears. Lugh was a Sun God and a warrior King. The tradition of warrior kings is passed down through legend. One Sir Gawain slew the Green Knight in Lud's Church, just west of Gradbach,"

Aren't Sir Gawain and hos Green Knight fictional?