From my own experience of SLC they will defer your loan for 3 years at a time if you prove that you are disabled. IE in receipt of any type of disability benefit.
When I started claiming DLA I sent the "Entitlement Letter" to them with a covering letter and they deferred me for 3 years.
The only way you can get the loans written off now is with a Doctors letter stating that you will NEVER work again. "Highly unlikely" won't cut it with them, I've tried!
I've just sent my S.A.R - (Subject Access Request) to them, just to see what they have on me. Once that's received I intend to send my letter from my GP and see if they will write it off.
Good Luck.
