Thats absolutely correct its the DeLisle commando carbine , I read about this some time ago heres the account and you wont get better info than this
http://www.rifleman.org.uk/The_DeLisle_carbine.htm
A couple of bits from this article , when they got the test model to London they wanted to know how good it was so it was test fired out of an office window at pigeons , also a .22 rf test model was made as a one off which was handed over to the National Army Museum as it was such a rare item but they lost it , so if you ever come across one in .22 rf :55:
By the way you will need a very fat wallet if you want to buy a modern repro and even more to try and find an original .
Dave