Lest we note, Mr. Beneltrain, GMT (or Zulu) does not make any adjustments for anything. During the period that Standard Time is advanced (or commonly known as Daylight Saving Time) the GMT variance will, if positive will be reduced by one hour, if negative increased by one hour.
As a ready example, during the winter period, the variation between Philadelphia's local time and GMT is 5 hours. However, when time is advanced, such as it last was at 201A April 2 2006, that variance becomes 4 hours. Since the British Isles do not advance their local time until the end of this month, the time difference between Phila and London is presently 4 hours. However, such will return to the customary 5 hours when the British Isles (UK and Ireland) advance their local time.