Depends on where you study tbh.
I've been told by some mathmos that the difficulty is insane and doing well in tests like STEP/AEA didn't necessarily mean that doing the degree would be manageable.
On the other hand, at some institutions, Further Mathematics may not even be required so you may spend some of the first year doing a recap of material you're already familiar with.
Either way, as long as you maintain a strong work ethic, it's likely your odds of doing well will be good.