This is a common misconception. The voltage regulator has NOTHING to do with spark or running. Everything runs off the battery, the charging system (alternator and regulator/rectifier) then recharges the battery. If the battery is completely dead you may have a regulator problem, but things would gradually wind down: spark would get weaker, affecting running and the lights would gradually dim. The key word here is gradually. Your problem was almost instant.
To run an engine needs lubrication, compression, fuel/air mixture, and spark at the right time. So these are the things you check. MAKE SURE YOU HAVE MORE THAN A SPLASH OF GAS IN THE TANK. I get 2 or 3 frantic calls every week that are fixed by putting a gallon of gas in the tank. Drain the carb and make sure there is clean gas in it. Check the air filter for obstructions. Check the oil level. Charge the battery. Remove the plug, cover the hole with your thumb, and spin the engine with the kick of electric start. You should be able to feel a big air pulse on (and blowing past) your finger. Put the plug in the cap and touch it to the fins. Spin the motor and check for spark.
Which ever test fails is the area for further work.For instance a common cause of no compression is a bent or unseated push rod. If they all check out then you have a timing or internal carb issue.
Most of these calls on the Enfield are traced to an ammeter wire, a battery ground, the ignition switch if it is electrical. Most of the rest are a dirty carb.
Check these basics firs, then get back to us.