Here you will links to fourth year projects which I have proposed. Some of them are suitable for students doing Combined Degrees in Mathematics and Physics, but most are for Single Degree Mathematics students.
A student doing one of the single degree projects is expected to work 200 hours on the project with minimal supervision; whereas the work required for a combined degree project is twice that amount. Students are asked to write a report at the end, usually 15-40 pages in length in the case of single degree projects, and 20-60 pages in the case of combined degree projects.
There is also the possibility of a group project, but I have not proposed any of those yet.