Why divert
Sometimes the simplest answer to a drain in your footprint is to move it. Water authority consent, design, and inspection all apply just as much to diversions.
Cost and time
Diversions almost always cost more than budgeted at first guess. Hand excavation in tight spaces, replacement pipework, new chambers and reinstatement add up quickly.
What to confirm in writing
Who pays for the diversion, who designs it, who applies for the build-over or diversion consent, and what happens if the diversion uncovers more issues.