Puccinia pragmitis (I think?)
I've always tended to ignore Rusts as I have always considered them above my pay grade.
However since they appear to be "flavour of the month", Here goes - - - -
I have to confess I am cheating big time! The latest edition of the Forayer which came through the letterbox yesterday included a piece on the Rusts on Broad Leaved Dock. Since I have plenty of Dock I thought I would give it a go, and came up with this specimen without too much trouble.
Whist looking I also came across this specimen on Silene dioica. Over to you Nigel on this one as I have no crib sheet this time!