Under FAA rules a safety pilot on a SPA class is allowed to log time. At Ari Ben they pair up two pilots and half your time is flying under the hood as "handling" pilot; the other half you are flying as the safety pilot. Hence under JAA rules only your "handling time can be logged". All the hour building is done at night.
Another thing to bear in mind if you fly and land at an over channel destination (Alderney, Jersey, France etc) then you can claim tax drawback on the fuel in your tanks. I don't know what the current drawback rate is, but when you consider the fuel capacity on an average light twin it can mount up to a reasonable amount.