It does generally vary quite a lot, although nigh on all unis follow a general baseline that is expected of a Maths degree. Some go into more depth, some go more into mathematical physics. Some also have more flexibility, e.g. a variety of modules. As an example of that, some unis offer modules in Mathematical Biology - other's don't. It's quite common to see CompSci modules, but again some unis may have different modules.
Most of the time you can find out what's offered on uni websites

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Again, difficulty is dependent wherever. (Also note that everything is dependent on uni for every subject). But also, difficulty you shouldn't be worried about: e.g. Oxbridge will have harder degrees than, say, Hertfordshire: but to get in, you need much higher grades and so while it will still be hard, it wouldn't be as hard than if you got in with say, 2 As and a B: it's all relative.
Contact hours will be generally dependent on lecturer/etc. But again, some unis have more time with students (e.g. a Maths degree at Cambridge has around 2 lectures a day, Monday-Saturday, and 2 supervisions/tutorials a week) which gives more help in that way.
Generally, it balances out. Hopefully this gives you an overview of that

. I would really recommend checking out websites though/student 'alternative' prospectuses, etc., to get an idea of how it is. Best of luck!