Fredxx wrote:

Is there enough clearance around or within the cowl, to put down the chimney
a heavy cord with a weight on the end?

Yes, a gap of about 2 inches nearly all the way round.

My thoughts would be to attach this cord to the brush and pull it up with
the rods trailing, rather than pushing the brush from below?

Now, that's a good idea if even the 1/2 inch flexible rods won't go up
with ease. Must remember that. Having spent roughly £100 on the
special flexible rods and brushes, this would be a way of ensuring they
can be put to use if they don't go up by being pushed from below.

Eddy.