Tim Lamb wrote:
Try fluesystems.com

They offer a modestly priced 6" brush. I believe you can use
conventional drain rods if you purchase the adapter bush.

Thanks, Tim. I see they advertise:

"Flexible nylon rods:- These rods are available in 1/2" diameter and are
designed specifically for use when sweeping chimney liners. They have
brass universal fittings and connect directly to the brushes without the
use of the adaptor below. Each is 1 metre long."

But they don't give any idea of price. Will email them and see if each
1-metre rod is less than £20 each.

No, can't you conventional drain rods. Have them already. Nearly an
inch thick and no flexibility in them for getting around the 45 degree
bends.

You could use a torch and a mirror to examine the flue further up. The
first few feet are likely to be hot enough to stay clean.

Right. So a clean first few feet doesn't mean it's clean much further
up. Thought that might be the case.

As others has said, be very careful.

Taking every precaution.

Thanks again.
Eddy.