Gents,
The choice to use copper, steel or this UK product called Kunifer is entirely up to you of course. Kunifer by the way, is a 90/10 alloy of copper and nickel--devloped to overcome the problems with copper. It is used nearly exclusively in UK and Europe and nearly unheard of in the USA. The problem with copper is that it works until it doesn't. Here a quote from someone describing a rebuild on a Mini:
"I had the long front-back brake pipe made up in copper and was in half a mind about the ones in the engine bay until one snapped when I moved it slightly (more like fell apart), so the decision was made for me. It is actually only about £20-30 for the whole set to be made up, don't trust old pipes even if they look OK."
Similarly another quote from another UK rebuilder:
Pure copper tubing work-hardens and becomes very, very brittle- especially at flare fittings. Under the cyclical loadings seen from brake applications, and in the presence of moisture (and possibly high concentrations of chlorides, if you live in a road salt area), they will almost certainly fail. They will tend to crack and fail right at the flare, generally with little or no warning. (Copper also catalyzes the auto-oxidation of fuel, the mechanism of sludge formation. Copper should never be in contact with fuel.)
Copper's day for fuel and brake lines has passed; but that doesn't mean you can't get it. In fact there are a variety of suppliers that make copper fuel line kits for Triumph, Jaguar, MG, Rover and other British Marques. But you won't have to do much research to hear the bad news about copper, and the good news about Kunifer as a replacement. But as long as you know what you are getting into so you don't have any surprises down the road, you should choose what you want.
Hope this helps.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored