That SMLE looks like it was the barn for a long time. I bet it would clean up well though. To tell you more about it... I need to know what it says on the left wrist, which is the strip of metal between the buttstock and the fore end stock. It might have a Crown, two letters, a maker mark, a year and then the model, something like Sht LE. But it all depends and when and where it was made. Also, on the opposite side of the barrel than the one you show up close in the photo there should be some markings as well. You can also check to see if the serial numbers match in the end of the round tip of the nosecap and the rear sight. And as all ready stated, I agree you will find the bolt and the full mag some where very near to the where the rifle was found. It will be up high and out of site... but easy to grab if you know it is there. That is what I call a barn gun. It is a gun you put in the barn in case you are out there or out side and need a gun quick. It is common up here in Maine for the old timers to do just that. I think it is a tradition that is still in effect in some parts.
With the magazine cut off, the British proof marks and the N serial number prefix, I will take a wild guess and say it is a ROF Enfield rifle made 1916 or before. If you could include a pic of the rear sight as well that would be great. I am wondering if it still has the rear windage wheel.