I used 'small-bore' copper radiator pipe (like you saw at B&Q) when my old Cav LXi's fuel lines rusted to the point of seeping petrol!
It comes in different diameters (if you look around in the specialist plubing places), but IIRC I used the 8mm.
It worked too! I'm sure there'll be people on here worrying that the fuel pressure is so high, it might split the copper - well I worried about this, but never had a problem. BTW, anyone know just how much pressure would rupture that sort of pipe...?
I remember Vaux wanted STUPID MONEY for the proper pipes, and I thought I was the only clever barsteward to have come up with that 'cheat' using copper pipe!
the pressure wouldnt worry me at all, but i am sitting here thinking maybe the pretrol might slowly eat away at the copper, maybe slowly introducing copper elements to the fuel, aahh i dunno.
Before you say the standard pipes are copper, i'm not convinced, cause copper doesnt corrode like my old pipes had.
Anyway, i got 2 lengths of 8mm stainless steel hydralic line from my local hydraulic specialist (dunlop hiflex) which cost 6 pounds a metre, takes up to 1000psi (over kill tastic) and will last longer than the rest of the car.
I asked a Plumber about this a while back as was worried about copper pipe (microbore) being able to take the pressure. Was told that when used in heating systems they test it to over 5 bar - so would be OK for fuel injection use.
The stuff Vaux have is steel and its not easy to bend into shape.