A gas turbine engine comprising: a first shroud block including a mounting slot ; a blade outer air seal supported within the mounting slot ; a seal disposed within the mounting slot providing a seal between the blade outer air seal and the mounting slot ; and a first anti-rotation tab attached to the first shroud block within the mounting slot for constraining movement of the seal within the mounting slot , characterised in that : the first anti-rotation tab is disposed at a first end of the mounting slot , with a second end of the mounting slot distal from the first end not including an anti-rotation tab such that the seal may be slid from the second end into abutment with the first anti-rotation tab at the first end of the mounting slot ; and in that the gas turbine engine includes a plurality of shroud blocks with a corresponding plurality of anti-rotation tabs , each disposed at the first end of each mounting slot , such that the seal disposed within the mounting slot of the first shroud block is contained at the first end of the mounting slot by the first anti-rotation tab disposed within the first shroud block and at the second end of the mounting slot by a second anti-rotation tab disposed within a corresponding second shroud block . a first shroud block including a mounting slot ; a blade outer air seal supported within the mounting slot ; a seal disposed within the mounting slot providing a seal between the blade outer air seal and the mounting slot ; and a first anti-rotation tab attached to the first shroud block within the mounting slot for constraining movement of the seal within the mounting slot , characterised in that : the first anti-rotation tab is disposed at a first end of the mounting slot , with a second end of the mounting slot distal from the first end not including an anti-rotation tab such that the seal may be slid from the second end into abutment with the first anti-rotation tab at the first end of the mounting slot ; and in that the gas turbine engine includes a plurality of shroud blocks with a corresponding plurality of anti-rotation tabs , each disposed at the first end of each mounting slot , such that the seal disposed within the mounting slot of the first shroud block is contained at the first end of the mounting slot by the first anti-rotation tab disposed within the first shroud block and at the second end of the mounting slot by a second anti-rotation tab disposed within a corresponding second shroud block . the first anti-rotation tab is disposed at a first end of the mounting slot , with a second end of the mounting slot distal from the first end not including an anti-rotation tab such that the seal may be slid from the second end into abutment with the first anti-rotation tab at the first end of the mounting slot ; and in that the gas turbine engine includes a plurality of shroud blocks with a corresponding plurality of anti-rotation tabs , each disposed at the first end of each mounting slot , such that the seal disposed within the mounting slot of the first shroud block is contained at the first end of the mounting slot by the first anti-rotation tab disposed within the first shroud block and at the second end of the mounting slot by a second anti-rotation tab disposed within a corresponding second shroud block . <EOS>