I've heard the very same legend applied to Freebrough Hill close to where I live in North Yorkshire
http://www.yorkmoors.com/ekd0488.htm The Sleeping Knights of Freeborough
One legend suggests there is a deep pit shaft running directly from the summit into the depths of the earth, and that this was used to bury hundreds of dead soldiers and horses after bygone battles.
Some say it contains the bodies of those who died during the black death: indeed a grave was found on the side of the hill during the last century. This was made of whinstone blocks, which had been carried three or four miles to this site, thus indicating a grave of some importance.
The is the legend of Edward Trotter who lived in a small holding in Dimmington.
When chasing a lost lamb he found a large hole the size of a badger sett. On crawling inside the hole he found a tunnel running deep into the hill. The tunnel grew larger as he passed through it. He then came across a huge chamber with a heavy oak door studded with iron with a large iron handle.
On entering the door, Edward encountered a man in chain mail with a long spear in one hand and a sword in the other.
The man awoke and stopped Edward from running away.
The man commanded Edward to be quiet. Edward notice that there were more men in similar dress all asleep and seated at a round table.
The guard informed Edward that "we are King Arthur and his Knights of the round table, we are sleeping until our services are again required.
He then swore Edward to secrecy and told him to leave.