This is a new old stock genuine Rover hose for the Mark II Rover 3 Litre and the P4 Rover 110. The part number is 530441 and it is the hose which goes under the inlet manifold.  In Rover terminology it is the "adaptor to inlet pipe hose". These are now really rare as original Rover items with the original style string reinforcement.

If you have any questions please ask.