Definitely Laminated Steel Paul, and remarkable similar to "Silver Steel". I can't image Greener would have let a pair of his proprietary tubes out of the shop!
They may actually be "English machine-forged 3 rod Laminated steel" which was the winner of the Phase 1 test of the Birmingham Proof House Trial.
Scroll down about 1/3 here
https://docs.google.com/document/d/1...EK8OtPYVA/edit