I wouldn’t try it, there are rangers covering everything from the Ribble estuary south to the military range at Altcar. There are actually byelaws prohibiting camping so it isn’t just trespassing, you could receive a fixed penalty fine. The properties are run by the council, The National trust and the Nature Conservancy Council, all of them are well equipped and take the no camping thing seriously.Have you looked at some of the coastal regions Southport to is it Ainsdale? I wonder if you could sneak an overnight in the dunes area or the woods with the squirrels. Used to live not far from Banks, the other side of Southport, so vaguely recall that's a nice area to walk.
I would add to this. Don’t light a fire because the smell if smoke carries a long way on the sea breeze and they take it very seriously. Be careful where you park. Overnight parking around the National Trust or Formby point sticks out like a sore thumb. The access down lifeboat Rd and car parks are well known for cruising or dogging so the police watch them. Victoria Rd is like millionaires row so again, the police watch it.Arrive late, leave early, leave no trace, dont be a [insert choice of phrase here]
Many of us dont have the luxury of owning land or having a permission. I regularly sleep on council owned woodland.