Grahame. You are bucking the current Mantra.
Buses compete with other buses and trains, trains compete with other trains and buses so any form of collaboration is anti competitive.
Yes, I know; many a true word spoken in jest. It may be the current mantra, but many times / on many corridors it's just plain wrong.
Let's take a corridor I know well.
Northbound
Monday to Friday trains at 05:33, 07:19 07:52, 10:01, 12:32, 14:32, 16:41, 18:55 and 20:22
Monday to Friday buses at 07:02, 08:06, 08:24, 08:53, 09:28 and every 30 minutes to 14:28, 15:48, 16:49, 17:15 and 17:52
Southbound
Monday to Friday trains at 06:27, 08:59, 11:20, 13:29, 15:29, 17:51, 19:06 and 21:00
Monday to Friday buses at 06:30, 07:20, 07:35, 08:25 and every 30 minutes to 13:25, 14:05, 15:05, 15:45, 16:30 and 17:30
The train is point to point (and predominantly passengers go beyond the two endpoints I have used); the bus is linear and serves perhaps a dozen or two intermediate stops. Both have grown in ridership and frequently over the years and really they don't compete. Train or bus operators might say to themselves "if only we could get the bus or train passengers onto our train or bus" but in reality the number to transfer would be very limited. Where you do have an opportunity to get
more bums onto existing seats is to encourage people to go out by rail and back whichever way they like, or out by bus and back whichever way they like.
Ticketing for such an arrangement? Buy a return ticket for the outward journey and it's valid back either mode. Fare is kept by the seller of the bus or train ticket; initial thinking suggest to me it would balance out and everyone would be a winner. More passengers on public transport, more income for both operators for no extra seat provision. Complexities? Yes - how do we get there from here, what about season tickets and weekly passes. How about people who go outbound all the way by train, but on the way back transfer at the northern station to a bus (it's a junction with plenty of other trains ...). How about other ticket types (Operator day tickets, rangers and rovers, etc)?
Except of course in London. (I wonder why?)