If there's soil at the bottom of the wall, I'd suggest Hydrangea anomala - you probably would need to remove the mesh you've got there because its a self clinging vine and won't appreciate mesh. Deciduous climber with white flowers in summer, does really well in shade.

Update - on looking more closely, maybe that's not mesh over the trellis section, but some sort of pot supports...

I agree with bamboo- I've just bought one of these hydrangea and only had it about 9 days and already it's climbing over where I need it to and the ends I clipped off have new shoots appearing too :) definitely recommend it

Sorry I was not very clear with my question. I was looking for something to go in the pots.

I wondered if that's what you meant - the trouble is, those potholders won't hold very big pots, so anything permanent will outgrow that size pot quickly. Okay for temporary bedding type plants, but not okay for permanent shade lovers (many of which disappear in winter anyway, especially as you're not keen on ferns). Hanging much larger holders with pots might not be an option, the trellis may not take the weight anyway...

Thank you for that. Back to the drawing board.

I had a nice display of hanging basket plants up there a couple of years ago. They did surprisingly well despite the aspect. But they were a real faff to water. So I guess replanting each year is the answer.

Do you think small trailing begonias will be forgiving if they don't get watered occasionally. I was thinking, one tuber to a pot and hang them close together. Alternatively just using the 'Filler' type trailing plants. Would the ones without flowers be more tolerant do you think.

You could do a mixture of the two so there's not just one thing to look at and adds a bit more interest to that area :)

IN shade, you might get away with not watering for a day, but if its hot and dry, probably not, specially once they're fully grown. I expect you know which bedding plants do well in shade by now, but the basic list is fuchsia, lobelia, pansy, impatiens, begonia.Fuchsias will be less forgiving with infrequent watering...