Damien has posted most of the relevant facts. Shortly after this accident we were issued with modified leg restraint garters that had removable D rings to cope with when the cords would not disconnect from the seat pan. A friend of mine flying Scimitars at the time said that when the aircraft sank the pilot was free apart from his leg restraints.
In those days the emergency egress drills on the surface recommended that you undid everything before getting rid of the canopy on the basis that it provided protection from fire on the ground and water coming in at sea.