Not a problem Stu, love to help.
The T posts are an inexpensive way to run fencing around large ranches and such. I doubt England has many of those left. Here there are still Ranches/Farms passing 10,000 acres. You can't fence in ranges of those sizes with standard/beauty fencing unless you have a major tech company in your back pocket!
I'm surprised you can't find T posts there, like you said, they are all over the place here. I'd think China would be trying to push them all over the planet.
A fairly common alternative these days is the simple thin wall galvanized steel pipe just driven into the ground. They last okay and are easy to put in. You can then use wire, boards, chain link, or slip covers and panels... lots of options. So it's pretty popular.