It was a military surplus rifle that had been "sporterized" (mainly by cutting the stock down to a more civilian profile).
The Enfield has an interesting history: Back in the period leading up to WWII the British mmilitary had a good idea the war was coming. The army was armed mainly wiith the Lee-Enfield bolt action rifles and they knew they needed a good slect fire automatic/semiautomatic rifle to replace them, least they be outgunned. But they debated over WHICH design to pick for so long that, when the Blitzkreig brought the Germans into a faceoff with the British, the autos weren't yet deployed.
It turns out that the Lee-Enfield action has a number of features that make it VERY much faster to operate than other bolt-action military weapons of the time. The bolt has a very small throw angle. It has rear, not front, locking lugs (out where there's lots of clearance and little stress and opportunity for dirt to gum them up). The action is almost glassy-smooth. The bolt ball is located where it can be opened by the thumb, while slapping it closed with the palm, doesn't require accurate positioning of the hand, and guides the hand back to the correct position to fire, letting the user's attention remain on the target scene and sight picture. It cocks on closing (rather than on opening as Mausers do), dedicating essentially all the energy on opening to case extraction, rather than splitting it with spring-cocking and keeping the opening and closing work closer to equal.
The result is that, with a modicum of practice, a rifleman with a Lee-Enfield can achieve higher firing rates than the operator of a machine gun. (Machine gun rates are deliberately limited to make them easier to control and aim, avoid wasting ammunition, and reduce overheating, burnout, and jamming.) It can't keep it up as LONG, because the Lee Enfield has a small, fixed, magazine. But it can fire a couple fast, controlled, bursts - just what is needed in many situations - using a powerful rifle cartridge.
By comparison the Germans were armed with things like the recently developed "assault rifle" - a short-barreled select-fire rifle (for easy handling in cramped hallways or popping up out of a tank hatch), firing a low-powered cartridge. (Militaries had figured out that a gun should be designed to WOUND, not kill: Kill a soldier and you take one out of action - wound him and you use up him, his buddy, a medic, and a lot of infrastructure and supplies taking care of him and shipping him back home.)
The Blitzkreig stormed across much of Europe and encountered only limited resistance, typically armed with the likes of the slower bolt-action Mausers. Then they came up against the British. They knew the Brits were armed with bolt-actions and believed their own propaganda about their lack of resolve. So they expected to sweep them up as they had their previous encounters. They came charging out, and were blasted back, repeatedly, by withering fire. There are records of communications from the front where the officers were claiming all the Brits were armed with machine guns. (I hear one of these records is a recording - with the officer in question being killed in mid-message by a round from one of those Lee-Enfields.)