A catheter comprising an inner sleeve and an outer sleeve surrounding the inner sleeve, the inner and the outer sleeves being longitudinally displaceable relative to one another to enable the catheter to move from an open state to a closed state, each sleeve having a distal portion and a proximal portion, the catheter further comprising a retainer which is open in the open state, and closed in the closed state, the catheter further comprising a lock mechanism comprising lock formed in a lock portion of the catheter for locking the catheter in the open state, and a releaser for releasing the lock, the releaser being adapted to remove at least a part of the lock portion from the catheter.
