What tubing is it ?

CYCLESPORT1

I have just finished building up a winter bike with my first compact chainset, the frame is a Fort from the Czech Republic and is made with a very lightweight steel tubing, the top tube is round and standard steel size, but the downtube is oval and oversized, it could be 10 + years old, what I want to know is what was the tubing ?
I think Raleigh and Diamond Back used the tubing for there Cyclo-Cross frames some years ago.
I have had it resprayed so no stickers.