The RHS site says:

Anthemis tinctoria
Echinacea purpurea
Helenium
Phlox paniculata
Sedum (upright, strong-growing forms such as 'Herbstfreude')
Solidago

It adds that many late-flowering perennials are suitable.

that is so strange I was wondering too if there was a list somewhere. lol :O) Can you Chelsea chop Lychnis? as mine has grown very tall this year, think it is all the rain which made it get bigger and bigger. A list would be very useful.

thanks spritzhenry and oliveoil, the flowers are a little smaller on the daisies that I cut back in May, and have not grown quite as tall, but so many more heads to each stem, I think it might be worth risking cutting back alternate stems on some plants, that way you won,t spoil the full plant

Yes, that's recommended as a 'technique' - or else chopping the front ones, leaving a two-tiered effect.

Lychnis isn't mentioned specifically, Olive, but I suppose you could try it next May??

think I am going to try it. This year was a strange one as most of my plants were behind because of the wet we had but I shall definitely try it next year even if it is only every other one, they have grown that tall and straggly (still very pretty though) lol thank you :O)

Which Lychnis is it? You'll have to let us know how it goes.

I will have to look Spritz no idea which one it is and I will certainly let everyone know how it goes if I dare do the chop next year, I will be brave I will be brave I will be brave lol :O)

Hi Spritz think it is L. Chalcedonica, and reading the rhs information on it it looks like it can get to be as tall as this of mine is. Will try and find the label in the border tomorrow and double check its name. :O)

Is it scarlet? I'd be pleased to hear that you can give it the 'chop', as mine are tall, and tend to flop.

yes its the Scarlet one Spritz, did find the label and I was correct, but on the label it states to 34 inches lol. Its 5ft tall already lol. and propped upwith canes etc to keep it upright, but I do love it so it will stay. lol :O)

I don't think mine are 'quite' as tall as that, but then, I haven't measured them! lol.

We are surrounded by tall trees and hedgerows so think the plants all grow taller than they would do if more light was available. Just one of the problems of gardening in a woodland setting. But after saying that I wouldn't swap it for anything it is so peaceful here. Well most of the time. lol :O)

Where we lived before, we had 8' potato haulms!!!! LOL. That garden was surrounded by trees, so I had to get used to shade -gardening.