If memory serves (I don't have immediate access to my old sourcebooks atm) the Pendragon was a demagogue who appeared around 2062. He was uncatchable by the authorities and caused many near-miraculous events and inspired a company to form in preparation of his coming.
He vanished after helping overthrow the Lord protector and meeting with the Queen. Since then there's been rumors that he was engineered by the Queen to cement her power, or perhaps he was the real thing and may come again in England's time of greatest peril.
...ahh yes, the mysterious and elusive chap referred to as The Pendragon. He appeared in a couple episodes of my old 3E UK campaign. Never knew what happened to him after 3E went out of vogue. Don't recall that much detail was given about him or the situation in the UK in
System Failure.
So Lord Marchment is no longer the LP and Queen Diana has succeeded King George VIII. Curious.
...and what of the Island, Lyonesse