I'm fairly sure it is tig welded. This one is Columbus Thron tubing with canti brakes and the lady I bought it off had gearing for doing CX on it. I think some nicer quality components came off it too, it has Campy hubs, deore FD, sora RD and lower end shimano STIs now

From what I have learned , Athur Caygill is a small English frame builder reasonably local to me and quite well respected by "those that know". Has a shop about 30 miles from me, I may call in and see what original spec was.

I'll post some better pics tonight if anyone is interested