I would look at this book if you are interested, in design and construction. Building Construction Illustrated
Edit: This is a book we use at my architecture firm, and Is recommend to read through it at least once before taking the ARE(architectural registration exam), in the States. It goes through foundation types, truss', and framing. I would recommend it.
There were two books that I had for school that I still reference at work today. The one most helpful for details is "Building Construction Illustrated" by Francis D.K. Ching. I have the 4th edition, but I believe there is a newer one now. I'm not sure just how different standards are in the U.K. but it has all different kinds of details from wood/steel framed construction to CMU & masonry as well as different foundation types. At the firm I work for we do a lot of work with production home builders and I find a lot of information in the book extremely helpful.
Here's a link to the fifth edition on Amazon. It looks about the same as the one I have just updated.
Francis Ching has a whole series of very easy to understand books on architecture. Some of his books are pre-requisites for aspiring architects
Check out: https://www.amazon.com/Building-Construction-Illustrated-Francis-Ching/dp/1118458346
Look at your local library if you'd rather not purchase it.
It's an interior partition wall by Ching's definition.
NFPA would call it a partition, and a fire barrier as it (could reasonably be) assumed to be constructed using a standard UL assembly like U419 and simply not extending to the underside of the deck.
Based on life experience, the ceiling was once 6" lower than the top of that wall. Just above the hung ceiling in most offices the walls are like this. They don't go all the way to the floor above. You only take the wall up to deck to create a fire separation (a Firewall) or for acoustic reasons of sound transmission. At some point someone hung a new suspended ceiling system higher than the old one and ended up exposing the top of the wall.
Side note, you'll see that there are some bare studs going all the way up. This is based on the framing partition max height tables which dictate how often and what gauge framing must extend up to create a system not subject to overturning motion.
Building Construction Illustrated by Francis Ching is an amazing reference for very detailed & accurate construction drawings & general details.
My favorite is Ching's Building Construction Illustrated: http://www.amazon.com/Building-Construction-Illustrated-Francis-Ching/dp/1118458346
I used it when taking my licensing exams. Wish I had it in school.
This book has some good info in it. It is where I get a lot of my dimensions.