The coil in the pipe was a bit of a problem to unwind. In the end I would it up again and started from the top unscrewing it as I went. Roots at the top made it hard to dig a trench and then grass clumps towards the bottom.
I dug down about a spade length as I didn't want cattle to dig it up. I didn't mind the line not being perfectly straight as hopefully when it is grassed over it won't be noticeable.
I will plant some grass seed over the next week and then it should look fine. It will be very important in the summer to have water close at hand.