I would suggest in the first instance a very strongly worded letter to the hotel setting out your position. In that letter I would state that should you not receive a satisfactory response from them within 10 business days you would proceed to rate and share your experience of their hotel on all possible sites (including Trip Advisor) warning future customers of the experience that they can expect. Inform them that you will also let the local newspapers know as well as national newspapers should there be in any interest.
Express your disappointment that they have not lived up to the basic expectations you had of them to ensure your day was special.
In terms of the legal situation, unfortunately they can disclaim liability for loss of property. However, if this is theft, as it appears it could be - you should also (in your letter) ask for a copy of the CCTV for review. I would phrase your request like this "In addition to the action I shall be taking to warn your prospective customers of my experience I will also be pursuing my own investigation into this situation. As is my right under the Information Commissioner's CCTV Code of Conduct, I request copies of the CCTV images/video from the applicable cameras covering the areas in question."
Whilst you have a right to ask for the CCTV, they do not necessarily have to comply
This letter should be sent special delivery and be typed out formally. Hopefully this will ratchet up the pressure on them.
If this fails then I would contact a local solicitor.
As to the insurance, it will depend entirely on your policy and its wording.
Hi - is there anything else I can help with? If not, I would be very grateful if you could close this question. Kind regards