So why does he have a high pressure on his hot tap then? That's what I'm asking you.
He doesn't have high pressure on his hot, it has higher flow than the cold. As to why it's higher on one than the other - it's anyone's guess - air lock, crud in the pipe, isolator not fully on, tap design, etc, etc, etc.
Unless he has more than that magic 5m of head, one of the above problems, or a combination of several, may give him the symptoms he has. With adequate head a slight restriction, etc wouldn't be so critical.
He has a considerably higher flow from the hot tap yet the hot water travels all the way down to the tank near the boiler where it's heated indirectly then all the way back up to the bathroom and out of the hot mixer tap at considerably higher output than the cold tap that simply comes down from the loft??
I think you need to do more than a short course in plumbing mate.
Joe, if you can't understand what I have posted, there's little I can do about it.
At least you can go back to arguing the toss on General Discussion, hopefully having grasped the difference between pressure and flow.
If you want to showcase your lack of understanding of basic plumbing principles, please don't hesitate to post here again.