If the stock is jigged correctly with clamps, it can be straightened and when cooled, it will stay straight. That is until the next time that it gets hot. And there lies the problem. If you want to shoot the rifle much, that stock might give you grief again later.

It can be pulled back straight, but doing so will put internal stresses back into the wood just waiting like a spring to be released.

The stock warped because there were internal stresses inside the wood, which could have been there since it was cut from a tree. Then something happened that allowed them to overcome the natural stiffness of the stock. If say it got hot, or if it got or got wet. 

I was given a bunch of woodwork that had been stored for years in a chaps basement, nice and dry in the furnace room, lent against the wall beside the furnace. Every single piece had a warp. However, it was rare enough to warrant the effort to rescue. 

Still lots of nice straight Mk.2 stocks out there. All depends on if you like tinkering and how much effort you are prepared to put in. 

In service, a unit armourer would likely just replace the stock and be done with it.

So your stock is fixable. It doesn't have to be straightened all in one session. The wood will warp in two directions in relation to the axes of the rifle. Usually there is a twist in that warp that manifests itself. It can take a bit to tweak it in the right directions. A real challenge at times to do, but doable. Patience is key. 

The fun part is in figuring out the clamps and jig. The steam box can be made of wood or anything that will contain the steam for a few hours (Press board is not good!). A Coleman stove and an old pressure cooker with a rubber hose fitted makes for the perfect steam generator.

Oh yeah, and the steam box will remove the finish on the stock. Pop up and raise all the dents and raise the grain. Hence gunsmiths using the technique of hot oil which doesn't disturb the finish on customers expensive sporting guns.