JAR-FCL 1.080 shall give you all the answers you need:
JAR–FCL 1.080 Recording of flight time
(See IEM FCL 1.080)
(a) Details of all flights flown as a pilot shall
be kept in a reliable record in a logbook format
acceptable to the Authority (see IEM FCL 1.080).
Details of flights flown under JAR–OPS 1, may
be recorded in an acceptable computerised
format maintained by the operator. In this case
an operator shall make the records of all flights
operated by the pilot, including differences and
familiarisation training, available on request to
the flight crew member concerned.