Under JAA rules only one person in an aircraft may claim PIC at any time. If you are under instruction (e.g. for an IR) the instructor is PIC and you are P/UT. If you are flying under the hood with a safety pilot and not receiving instruction, you can claim PIC but the safety pilot cannot (or vice versa). Consequently, the various hour-building packages available in the US that depend on both pilots claiming PIC, which is permitted under FAA rules, are not suitable for JAA purposes.