After digging the trench I decided to get some flexible ducting as there are lots of big stones, some quite sharp, and I didn't want to risk any damage to the cable. It's a 50 metre length so not quite long enough, but I do have some grey BT duct left over from when we built the house over 20 years ago so can use that to make the full length up.

The ducting is 50/63 with a draw cord pre-installed. How difficult will it be to pull the fibre through? I have no idea how heavy the cable is and I'm trying to decide whether to fill over the ducting before the cable arrives. It's not a straight run but there are no tight bends either.

Depends somewhat on what type of fibre will be used, though neither is at all heavy, BFT being lighter than the connectorised stuff.

You say there�s no tight bends, so that�s good, make sure too that the transition between duct types is smooth inside so as nothing might catch ... then I�d say you can backfill with impunity.

Thanks Zarjaz, that's what I was hoping.