This isn't deferring, it's called an interruption of study and each uni will have its own regulations on how it's handled.
I suggest you check this out before you go any further.
Where I am, the student has to make a formal application in writing to and this is considered by the Dean. Your Personal Tutor may be asked for their opinion on whether you should be granted it.
There is no right to interrupt - you have to make the case for why.
Obviously, if your academic profile is sound it's more likely to be accepted.