Paul's relationship with his father is something really complex, and it's a whole other topic that I don't want to get into right now, so I'll just talk about what Jim thought of John. Jim never liked John. From the very beginning, he thought John was a bad influence on Paul. He even tried to get John out of his own group, according to John himself:

"And his dad was the whole thing. Just simple things: he wouldn't go against his dad and wear drainpipe trousers. And his dad was always trying to get me out of the group behind my back, I found out later. He'd say to George: 'Why don't you get rid of John, he's just a lot of trouble. Cut your hair nice and wear baggy trousers.' [...] His dad told him to get a job, he fucking dropped the group and started working on the fucking lorries, saying, 'I need a steady career.'"

Jim was also reportedly "delighted" when Paul got Dot pregnant, which I believe had to do with the fact that this would force Paul to settle down, leave the band, and possibly get away from John. That bad blood seems to have lasted a long time because, in 1971, Ray Connolly was trying to deliver a friendly letter from John to Paul. One day he phoned Paul's London house, and Jim was the one who answered. He immediately and rather angrily shut him down, telling him not to get involved and that "things have already moved on." But I do think there was more to it than simply John's reputation, Jim worrying that he would be a bad influence and get Paul into trouble (which was very true, lol). I'm sure many of you remember that last year I mentioned receiving some second-hand information about someone who spoke to Jim around 1968. Jim apparently still didn't like John. According to this person, Jim said that he and Mimi used to be in somewhat constant contact in the late 50s because neither of them wanted their boys hanging around together, and both became increasingly uneasy about how intensely close they had become, and how quickly it happened. Jim was especially concerned because Paul stopped paying attention in school and was constantly sneaking around to meet John. The person who spoke to Jim got the impression that Jim believed something "taboo" might have been going on between them, and that this was one of the reasons he didn't want them spending so much time together. Colin Hanton also said that Jim made a rule that Paul and John couldn't be alone together in the house, that Jim himself had to be present for John to come inside. But, as we all know, whenever Jim was at work, John would come over anyway. According to Mike McCartney himself, John and Paul would often give him money to go to the movies so he "wouldn't interfere."

Something else I've noticed is that Paul often seems reluctant to admit either that Jim didn't like John or that he and John used to hang around the house while Jim was away at work. Paul does often say that they skipped school to play guitar and write songs together, but he usually doesn't specify that they HAD to sneak around behind Jim's back. Howard Stern actually brought this up in 2013, and Paul sounded a little hesitant:

Howard: Your father, by the way, didn't want you hanging around with John. Paul: Uhh... he... he didn't mind... he didn't mind John, you know. Howard: Didn't he say that John was a bad influence and you had to sneak out and meet with John when you guys were young kids? Paul: Well... almost, you know. But... by the time I met John, uh... I had some say on the matter.

And to end on a rather funny note, look at the Beatles picture in the background. It actually looks like Jim deliberately hid the right side of the photo—the part where John is supposed to appear—behind the other frame 😂