There was once a monster single platform which joined Manchester Victoria and Manchester Exchange, and claimed to be the longest in Europe. Not intended for use by a single giant train though.
The famous "long" platform at Manchester was formed when platform 3 at Exchange station was extended over the River Irwell to meet platform 11 at Victoria, making a platform of 682 metres long.
It was in effect 3 platforms, with crossovers allowing 3 trains to be accommodated simultaneously. Platform 3 was at Exchange, 11 at Victoria and 11 Middle in the "No Man's Land" between!
The platform was useful for the lengthy nightly newspaper trains [when Manchester was a famous printing centre], as vans could draw up right by the side of the train.
During the day time, it was a handy covered walkway between Exchange and Victoria stations. I well remember being rushed along there by parents with heavy suitcases when journeying from Halifax to North Wales and back!
In days gone by, before track circuits, going beyond the starting signal, and drawing up, were common practice, so platform lengths were not a constraint except at termini.
Back in the day, drawing - up at short platforms such as at Lightcliffe or Luddenden Foot was a common practice with long excursions to Blackpool, formed of non-corridor stock. Very time-consuming, and a real bind on the return journey when you were tired and just wanted to get home!