If you are UK based you can use any of a number of UK insurers who are able to write policies for boats located in the EU. Suggest you try Topsail who can offer policies from a range of underwriters. However, do not expect massive savings. insurance for yachts has been losing money for underwriters for years and premiums are rising, particularly for the Med and Caribbean where the losses have been highest. Look carefully at the policies you, particularly if you want agreed value as not all policies are the same.