Probably a bit late for everyone, but as I was driving through the New Forest today, I pulled out of a junction and bang! stuck in first gear and full 360 on the gear stick! What the hell is going on here I thought. I knew it had to be something to do with the linkage so I pulled over and got investigating, and there it was, the socket had come away from the joint! (See picture attached)
I noticed it wasn't clipping on but just sitting on top, so I placed it on top and eased the car home and then removed the battery, battery tray, intake and relay box to get in and have a good look.
The problem was that red dial/switch/straight line thingy (Technical name for it) on top of the socket. Turns out it locks and unlocks, and that there in the picture is in the unlocked position, got some pliers and twisted it left, now it's nice and secure!
Not sure why it came off in the first place, but I did rescue the car from a second hand car geezer, so it hadn't been treated well at all, hence how dirty it is!
Hope this is of help to anyone