We saw Jeremy Corbyn sitting on the floor of a train, though it now appears that he sat there because initially he couldn't find two seats together to be able to sit next to his wife.
How exactly would renationalising the railways relieve overcrowding? Many lines are operating at capacity. If there are no more paths available you can't run extra trains. In many cases you can't lengthen trains either without major changes to trackwork, signalling and platforms. If fares were reduced, as Corbyn says they would be, more people would travel and overcrowding would be worse.
There are possible electronic systems that can squeeze a bit more out of the infrastructure, but they'd provide only a short- or medium-term answer. What we really need is more railway routes, or additional tracks, especially as railways approach the centre of large cities, where the pressure is greatest.
Those solutions will be expensive. Think of HS1 getting to St. Pancras, or Crossrail. Building new lines above ground will be controversial as well, since not many people will actually want the solution to be at the end of their garden.
Finding answers will need very careful thought and planning, as well as a lot of money. It's much easier to start arguing about ownership and structure. People on one side of the political spectrum advocate one approach, and those on the other side advocate something different. They then imagine they are doing something about the problem, but actually it's a distraction and diverts effort away from achieving solutions.