Door lock barrel

Latest saga in my now 3 year old Swift Challenger and the numerous faults.  Now hit fault number 22.  When looking my van and withdrawing the key, the lock barrel followed and left an open chamber.  Can slide the barrel back in and will lock but can be removed!

Im assuming a clip has come away at the back but has anyone had this experience or advice before I write off yet another trip to the dealers...that’s if I can even get it booked in?

Many thanks and picture attached of the back of the door mechanism