Alfred the Great acted as his own spy, visiting Danish camps disguised as a minstrel. In those days wandering minstrels were welcome everywhere. They were not fighting men, and their harp was their passport. Alfred had learned many of their ballads in his youth, and could vary his programme with acrobatic tricks and simple conjuring.
While Alfred's little army slowly began to gather at Athelney, the king himself set out to penetrate the camp of Guthrum, the commander of the Danish invaders. These had settled down for the winter at Chippenham: thither Alfred went. He noticed at once that discipline was slack: the Danes had the self - confidence of conquerors, and their security precautions were casual. They lived well, on the proceeds of raids on neighbouring regions. There they collected women as well as food and drink, and a life of ease had made them soft.
Alfred stayed in the camp a week before he returned to Athelney. The force there assembled was trivial compared with the Danish horde. But Alfred had deduced that the Danes were no longer fit for prolonged battle: and that their commissariat had no organization, but depended on irregular raids. So, faced with the Danish advance, he had to prepare to defend the kingdom. He parcelled out the land into small holdings which were given to the great nobles of the realm in fief. In return for a free gift of the land, the noble swore to perform military service. The king retained a large reserve of land in his own hands. By this policy Alfred managed to create a large army out of very little money. And when the Danes, having had their raids, were again assembled in camp preparing for winter, Alfred struck suddenly. He routed them with his little army and chased them back to their ships. The Danes were not to be seen again in England for many years.
The episode could reasonably be called "Royal espionage". For Alfred had done what no spy had ever done before in the annals of espionage - he had stayed in the enemy's camp and returned with valuable information.