CAA LASORS states that you can merge sectors if the time inbetween each sector is no more than 20 mins. (Not often the case). I've no idea how that works as you pretty much gain 20 mins logbook time for nothing.
Extract from LASORS 2008 Section A, Appendix D
e. A co-pilot acting as pilot-in-command under
the supervision of the pilot-in-command on
an aeroplane on which more than one pilot
is required under the type certification of the
aeroplane or as required by JAR-OPS provided
such pilot-in-command time under supervision
(see paragraph 5 below) is countersigned by the
pilot-in-command.
. . .
f. If the holder of a licence carries out a number
of flights upon the same day returning on each
occasion to the same place of departure and
the interval between successive flights does not
exceed thirty minutes, such series of flights may
recorded as a single entry.