Ah the reality of internet routing, it's a complicated web. In fairness I wouldn't describe the pings you're getting as "high", certainly you could say they're "higher" than what you expected but 20-24ms in a game is still better than good and not something they're likely to consider as a fault.
Often a large urban area like MK may need the fibre to connect back to more than one central data centre, so to me it sounds like your link just so happens to go to a different one and associated route from your friend.
I'll be interested to see if changing the IP produces an improvement, so hopefully you'll report back. Would be handy if you ran a few tracerouts - before and after the change - to help show any change in the path of your packets.