Abstract: An arrangement and method for integrating a high pressure riser sleeve 60 from the upper end of a high pressure drilling and workover riser 10 which is terminated by an upper BOP 20 close to sea level in one end and by a sub-sea blowout preventer BOP or a low riser package LRP close to the seabed in the lower end. Said high pressure riser sleeve 60 being installed, connected and integrated to the high pressure drilling and workover riser 10 and extending up to and above the drill floor 90, inside a low pressure drilling riser slip joint which is connected to the drilling and workover riser 30, 40, 41. The present invention relates to offshore drilling and well activities preformed from a floating drilling or workover rig or vessel 93. The invention specify a system and a method where operations can be switched from drilling with jointed drillpipe in a conventional manner, into performing underbalanced wireline and/or coiled tubing activities with full well pressure, much more effectively than with prior art.