Dear {council officer},
Thank you for your letter of 3 December in which you gave permission for me to place two geocaches in {Park}, Torpoint.
Further to your question regarding public liability insurance, neither Groundspeak Inc. nor The Geocaching Association of Great Britain provides this. It is not seen as necessary since every geocacher participates at his or her own risk and must agree to a disclaimer to this effect before obtaining access to geocache coordinates. A reminder of this and a link to the disclaimer is prominently displayed on each cache page. Thus the council carries little or no risk specifically in respect of the geocaching activity.
If you wish, I am happy to meet with you or your representative at the park to show you the proposed locations. Hopefully, this will allay any residual concerns you might have.
I hope this answers your question, but please do not hesitate to contact me again should you require further information.
Yours sincerely, ...