Percy would visit the Queen’s chamber every afternoon to see Anne. Henry may have seen it for himself. According to George Cavendish, who worked for Wolsey, Henry found out that Anne and Percy were in love and were planning to wed. Henry went to Wolsey and asked him to intervene. Cavendish says it was because Henry was ‘much offended’ and had ‘secret affection’ for Anne. That is why he had Wolsey move to break them up. This seems to be disputed by historians, but if Cavendish is correct, Henry was enamoured with Anne by 1523.
Poor Jane. She seems to take the blame for what Henry did to Anne from beginning to end.

Actually Anne and Percy had no right to plan a wedding for themselves. Neither of their parents knew about it, or at least neither of their parents were actively working toward a marriage for them. Parents negotiated marriages for their children. They didn’t get to choose. Thomas Boleyn was still trying to gain a contract for Anne’s marriage to Ormond. Percy had been bethrothed to Mary Talbot for 6 years. His father was furious with him.
Henry could step into any one of his noble’s marriage negotiations. However, it does seem as though this interference was personal. Wolsey according to Cavendish, berated Percy for thinking to raise a knight’s daughter so high. Percy thought she had a good enough background and said so. Wolsey then told Percy that the king had other plans for Anne. (Oh, okay then. Why didn’t you just say that in the first place? ) Percy gave in.

Boleyn said

Yeah I know Wolsey sent for Percy’s father who came down on poor Henry like a tonne of Bricks. Wolsey said The king has other plans for Anne does that mean that he had already decided he wanted her for himself as mistress.? But it still doesn’t make it right that their marriage was vetoed ok they shouldn’t have taken the law into their own hands so to speak, but if lard boy was only seeing Anne at that time as a protential mistress what was wrong with her marrying Percy?

Here is what Cavendish writes about what Wolsey said to Percy:
“The king’s majesty himself will complain to thy father on thee, and require no less at his hand than I have said; whose highness intended to have preferred Anne Boleyn unto another person, with whom the king hath travelled already, and being at a point with the same person, although she knoweth it not, yet hath the king, most like a politic and prudent prince, conveyed the matter in such sort, that she, upon the king’s motion, will be (I doubt not) right glad and agreeable to the same.”
Wow, Cavendish writes run-on sentences like Sarah Palin speaks them!
Whether Wolsey was making this up or whether there was a match that Henry had in mind, I don’t know. I suppose Wolsey could be talking about Ormond. I don’t think Wolsey was telling him the king wanted Anne and that’s why Percy couldn’t have her.
One reason I can come up with as to why Anne and Percy were not allowed to marry was the king said no! Another is, who did these two young people think they were that they could defy their parents and marry someone of their own choosing? Even if they were well matched it doesn’t matter. Defying your parents was not done.
I don’t know what would have happened if Henry didn’t find out about this. Most likely they would have married secretly and Lord Percy would have disinherited his son. These two young people would have ended up in disgrace.

probably worth taking the personal out of it – its probably jealousy on HVIII’s part, but its also proper politics: the Percy’s at this point own most of England north of the Humber, they are the first family of the North, and since the destruction of the Nevilles in the WotR they have no rivals – they are, in effect, certainly equally as powerful as the King in there home territories, if they back a war against Scotland that war succeeds, if they don’t it goes nowhere, if they back a rebellion or sit on the fence, then the King is in very deep trouble. Boleyn is a member of the House of Norfolk who are, coincidentally, in the top 5 wealthiest and most powerful families in England at the time.

there was bad blood between the Percys and the Howards from the Wars of the Roses, and such a marriage (though Anne herself was somewhat lower in status than Henry Percy, which doubtless would have upset the wider Percy clan..) would have secured an alliance between two very rich, very influential, and very, very old astistocratic families who made the Tudors look like something from a reality TV show. in banning such a marriage, Henry VIII may well be playing the jealous would-be-sutor, but he’s also avoiding a match between two families that together are probably as rich, and as powerful as the Crown.