My nice new stainless steel strap is now on the car.
In the end I used two trolley jacks to support the fuel tank - very easy. The tricky bit was getting the two forward bolts out and back in again. I had to use a mirror just to be able to see them! (car is on sleepers and I haven't lifted it high enough to get under the floor pan very easily).
Anyway, ta for the help chaps.