Aye, from Appendix B to Section A LASOR it seems under national rules in the UK you have to log instrument time. However if you are using the privileges of a JAR license you also have to log IFR time. The latter is sadly under a heading "Recommended information", but alas it is explained that it should be logged for JAR licenses. Checking JAR-FCL 1.080 then explains that you have to log IFR time as operational condition and may log instrument time if you really want to. The thing that muddles some things up is that some seem to be of the opinion that instrument time is only possible in IMC, however that is not the case, it is time whenever you fly solely in reference to the instruments, which in my opinion is pretty much always when airborne in a jet, even in full VMC my flightpath is maintained solely in reference to instruments.
Flying under an uk issued license therefore requires you to log both, for the purpose of JAR-FCL and most probably the coming EASA rules only IFR-time is required. By the way, i have known a CAA that argued one can only log instrument time when flying manually as the pilot needs to manipulate the controls himself to be in full control of the aircraft with the sole reference to instruments. Quite sad really, but they do have a point.