I've never heard that - and a search for Labour Union at Cambridge reveals no organisation I can find of that name. He was, I believe, a member of the Cambridge Union, which is the oldest debating society in Britain, but that's hardly a left wing organisation - it takes in people from both sides of politics. But he may well have been left wing as a young man - I didn't really know him then. He certainly isn't now.
Of course, on the other hand, we also know that servants hold his urine specimans during examinations, he has 4 eggs prepared every morning to decide which one meets his specifications and Diana got fed up with him throwing things at his valet.
I've had breakfast with him more than once. He does not have four eggs prepared every morning. That story comes from Jeremy Paxman, a BBC journalist, who actually said it was seven eggs. I've never attended one of his medical examinations, but I doubt the other stories are true either.
According to Wikipedia - through the Guardian, 2006: “The Prince has been known to steer clear of partisan involvement- allegedly ever since, as an undergraduate in the 1960s, he was warned off joining the Cambridge University Labour Club.” I well remember the flack at the time.
According to Paul Johnson, it was Diana who was upset with Charles’ treatment of his servants, particularly his valet.
Jeremy Paxman got his information about the eggs from a friend of Charles. Whether it is true or not, I don’t know. It just seems to fit with his imperial personality.
I was in England at the time the story broke that Charles had a servant hold his urine specimen during a routine doctor’s visit. It was carried by all the newspapers.
He’s not his mother.