Combined tickets

This doesn't apply just to the Picc, but I remember that in the early 1960s, you could go to Northfields station and buy a return ticket to London Airport. The tickets were white with green sides. On arrival at Hounslow West (the end of the line then, and it was also a District Line station too), the ticket collector let you through as the ticket allowed you to travel on the 81B bus to London Airport Central. The conductor on the 81B bus was meant to collect the used half of the ticket but very rarely did, so I ended up with 6 of them... On the way back, you showed the return half to the conductor on the 81B, and travelled to Hounslow West. At Hounslow West you could travel by the first train (Dist or Picc) to Northfields. These return stubs were nearly always collected at the Northfields ticket barrier.

I understand the same facility was also available at Boston Manor

Does anyone else remember this?
Does anyone have any whole or part tickets, or photos of them?
Was this facility available from any other Underground stations?
Was this facility available for any other combined rail/road journeys? (I have heard it was Northern line/Northern Heights)
Did this arrangement continue until the Picc was extended to Hatton Cross then Heathrow? If not, when did it end?

All info gratefully accepted

Castlebar