It is extremely uncommon for root systems to damage a properly constructed and well-maintained drainage network. There are cases where tree (outer) roots will seek the moisture associated with pipework that is already compromised (damaged). This is not the “fault” of the tree or roots.
Where the drain runs outside the boundary of the tree canopy it is virtually impossible for roots to have any effect on properly constructed and maintained drainage pipework.
We don’t normally undertake work to remove trees or roots for this reason (see above).
Private owners: Please note that the owner of the drain is responsible for upkeep. If they can provide professionally produced evidence that damage has occurred (camera survey or similar) they should engage their insurance provider who will advise.
Contract Holders: NB blockages to “our” drains are a DLO area of expertise irrespective of assumptions related to root ingress. It doesn’t matter how it’s blocked, a repair / inspection needs to be raised.