A method for permanent plug and abandonment of one or more offshore platform wellbores of an offshore platform and for decommissioning of said offshore platform, wherein said platform has a jacket and a topsides. Use is made of a marine jack-up type vessel. The method comprises: - arranging the vessel adjacent the offshore platform bringing the vessel in an operational position wherein the cantilever is movable in an extended position above the topsides of the offshore platform, - moving the cantilever into said extended position above the topsides and aligning the wellbore activities station with a wellbore, - performing a plug and abandonment operation involving the use of the wellbore activities station, - retracting the cantilever, - disconnecting the topsides from the jacket, - lifting the topsides from the jacket and placing said topsides on board the vessel, - operating the elevating units so as to lower the hull of the vessel into the sea and to retract the jack-up legs upward.
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