Paul said ....... "So, any suggestions as to how I might add an end-stop the
one end, and attach a hose/downpipe the other? ..."

Well easy to make a stop end, just hold a piece of wood against the end then
draw the shape of the inside of the gutter onto it, cut out the shape and
fit it with silicone or mastic.

if you can drill an inch hole at the other end, do so and thread a half inch
chain through the hole.The water will run down the chain and not splash all
over the place.
You may need to close this end off as well..

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk