In message , BigWallop
writes

If these blockages are a pretty regular occurrence, then it seems there
could well be a crack or break somewhere. Or it could be roots from a tree
or hedge that have grown through into the pipe.

It takes a year or two and the location has moved. I'm fairly sure it
must be debris and is now in the final section.

Do you have enough rods to set a half way mark in the longest run? If you
do, or can borrow some, then put a rope on the end of the rods and push it
in half way before letting it go. This can usually be done with a twist or
two of the rope around the end of a plain rod. Go to the other end of the
run and attach the corkscrew attachment to the rods. Push along until you
reach where the rope should and twist the rods around until the rope is
caught.

Yes. If it blocks in that stretch I'm going to call the professionals as
I am very nervous of making things worse.

regards
--
Tim Lamb