While Bookworm in post 13 seems to have a PANS quote that atc accepts responsibility when giving an aircraft a vector or a DIRECT (my bold) routing. However, this does not seem to include clarifying that atc assumes altitude clearance responsibilities if a descent clearance is given while on an airway.
It's just in a different section. 4.10.3.1 says:
"Except when specifically authorised by the appropriate authority, cruising levels below the minimum flight altitudes established by the state shall not be assigned."
I've always taken that to mean that assigned levels on airways must be at or above the MEA. It does, however, come with a strong caveat:
"Note 3 - The objectives of the air traffic control service as prescribed in Annex 11 do not include prevention of collision with terrain. The procedures described in this document do not relieve pilots of their responsibility to ensure that any clearances issued by ATC units are safe in this respect. When an IFR flight is vectored or given a direct routing which takes the aircraft off an ATS route, the procedures in 8.6.5.2 shall apply."
Which is about as useful as reminding pilots that they sit at the pointy end.