Why the fee?

FURTHER to his comments concerning the admin charge for the Anderton Boat Lift, Alfred Overton writes:

Just a further thought, as other facilities (eg Harecastle Tunnel) are on restricted passage at the moment, booking is required for passage.

Why the difference?

But no fee is required for those bookings, both Harecastle & Anderton have to be manned for a passage, so why the difference?

[As has been stated, both are part of the navigation for which a licence is already paid, and so there can be no further charge...]