Good question, and one which typifies the total confusion the CAA has managed to create with these ANO changes.
SI 2007 No 274 specifically amends the ANO to mandate the carriage in specified circumstances of fire extinguishers, first aid kits, landing lights, torches, life jackets, elt's, oxygen, etc but does not specifically mandate the carriage of life rafts.
However, the SI also amends the ANO to require that the commander of a UK-registered aircraft not flying for public transport "shall reasonably satisfy himself before take-off that the aircraft carries such additional equipment as the commander reasonably considers necessary for the purpose of facilitating the survival of the persons carried in the aircraft."
The exemption permitting the use of equipment not approved by the CAA or EASA subsequently announced by the CAA (and referred to by you) does, though, specifically refer to liferafts. You could, then, reasonably infer that the CAA believes liferafts to be mandated by that new 'commander's responsibilities' clause for flight overwater. But it's your call, since the legislation leaves it to "what the commander reasonably considers necessary."