It does work both ways but it would be helpful to have clarity on the hierarchy of needs as the whole bus thing is a nightmare from anyones point of view. As I said before, this is all about children, not buggies.

If I get on the bus with my double buggy and toddler in tow, I do expect people standing in that area to move over to let us park in the appropriate place. If they don't, expect an argument as I will exercise my childrens right to get on. If I can get a seat I will put my toddler on my knee in order to save a seat for an adult assuming the driver isnt speeding round corners at high speed, like the P4 drivers are prone to doing.
If a wheelchair user tries to get on subsequently, I will decide whether we can realistically get off and walk the rest of the way. That will depend on the distance and whether I think my toddler is up to it. If not, then we are staying put. Folding up a double buggy with three young children is not possible at all. I expect therefore that my children get priority status in that context. Its tough on the subsequent wheelchair user but other than not attempt to use public transport at all, theres no other solution. And I'm not prepared to stop doing it, despite the uproar and outraged facial expressions that might ensue.

Many parents these days use buses to get from A to B for a reason, not just a trip to the park. They may be trying to get back in a hurry to pick up another child from school or nursery.

I would still like to hear more about whether some of these ( usually mothers) people of disrepute can actually expect to be offered a seat if they fold their buggy as Ive seen so many examples on the tube where this doesn't happen.