It's been a while since I flew in the UK under CAA regs (been in the USA for six years) but it was my interpretation that whatever craft you fly, it's up to the PIC to ensure that a safety brief is carried out. Here in the US, you have to make pax aware of the seat belt operation and exits/methods of egress.
In the case of an airline, the safety brief is delegated to the cabin crew - but it's mandatory to my understanding.
I always try to pay attention during the briefing (even though I've heard it many times before). It's just being respectful of the crew who are trying to do their job.
What always amuses me are the people who settle in and remove their shoes straight away.... they've obviously never considered that they might need them on to get over broken bits of aircraft (that may be on fire) in a takeoff emergency.
John.