I had to move several thousand pounds between two family accounts a couple of years ago using online banking, and the palava they make you go through is amazing. I had the transfer be put on hold and the anti-fraud department ringing up, stating money laundering laws is why they have to do it. Had to get the other account holder to corroborate every little thing, give reasons why the money was being moved, double checking IDs, etc.
It was a simple transfer between two accounts with the same surname at the same bank FFS.