Use decent oil, gun oil if you can but not WD40 or one of the Teflon types. A copper 2p coin has always been handy for removing stuban rust. The forces use Red scotch bright (Defo not the green). One of the best things you could do is to leave oil to soak into the steel for a few weeks or more.
If the Enfield is a SMLE type, you must remove the forwood before removing the butt as the butt bolt has a square on the end and this locks into the forewood. If the forewood is left on and the bolt is turned, the forwood can/will split.