I had an issue recently where I sent what was effectively a full sus frame and forks to someone, but before collection was made I had an email from the agency (Interparcel) explaining that bikes are on their list of prohibited items.
I have now heard of someone else with the very same problem.
Their T&C's state: "Bicycles / Bicycle frame Prohibited with Interparcel services, Restricted with all others"
This means will not ship at all on an Interparcel branded service, but will ship but not be insured with any of their other re-sold services such as TNT etc, supposedly even if you pay for extra cover.
They changed their T&C's recently as we used to ship computer equipment with them. They tried to suggest that no couriers would cover/insure comp eqpt, however we found a few alternatives within minutes (not tried bikes). Told them we could no longer use them for this reason - now the same with the bikes so I guess I won't be using them again mostly for the above reasons. Don't know anyone on the bikes for now though.