Calor Gas BS EN ISO 12864 Annex M is withdrawn and been replaced by BS EN 16129:2013 Annex M which is similar with regards to LPG Regulators used on seawater boats. LPG regulators are different to caravan/general purpose regulators in two specific areas (integral over pressure relief valve and high corrosion resistance ) for a reason. Namely, the more arduous demands of the marine environment itself. Potential corrosion issues are well understood by many of us, however the need for gas regulators with an over pressure relief valve may be less understood by Westerly yacht owners.
Westerly and other sailing yachts can readily incline to angles sufficient to cause high pressure liquid gas to slosh around and breach the gas regulator causing an over pressure condition within the low pressure cooker feed pipe. Over pressure in the low pressure feed pipe to the cooker can cause gas to breach & leak past seals to either; collect in the bilges, or unintentionally ignite at or near the source of the leak itself (eg, cooker control knob). Both conditions are extremely hazardous.
For practical purposes there would be no justifiable reason for a sailing yacht fitted with an LPG system as described above to go to sea with anything other than a BS EN ISO 16129 Annex M compliant gas regulator correctly installed and fitted.
Such a regulator will provide longevity with respect to corrosion and a safe route away from the Westerly yacht (via a properly vented gas locker) for any gas discharged by the regulators over pressure relief valve.
Boats used inland don't tend to heel over, in general. In terms of the Boat Safety Scheme guide and the BS EN 10239 LPG installation standard, it might be that these documents are possibly lacking in the area of BS EN ISO 16129 Annex M regulators and there use/need on sailing yachts. It is possible these documents may not be promoting best practice if this is so. However this is no justification to doing anything other than the "right thing" on your boat, which is to correctly install a BS EN ISO 16129 Annex M gas regulator based on intended use on a sailing yacht at sea.
BS EN ISO 16129 Annex M marine gas regulators are available for under £50 it is sensible to fit the correct regulator for the intended use.