This really needs getting rid of (buying out, if necessary) - interworking reduces punctuality and reliability by causing an incident on one branch to affect another branch even if it needn't do so, and by making getting things back on time far more complex than just cancelling a round trip and leaving the unit and crew in a siding. The simpler the diagrams, the better.
It was a big part of the issue with the LNR cross-Birmingham working, and Avanti would be more punctual/reliable if it was avoided.