Not a true Geranium, but maybe Ivy Geranium (Pelargonium peltatum)?

Trailing verbena, petunias, annuals, stick some trailing ivy in there.

Trailing rosemary.

Lysimachia nummularia aurea (hope the spelling's right), common name Creeping Jenny. Stays quite flat so would need something taller in the middle. Sends out quite long trailers.

MBD's trailing Rosemary would be excellent. Will cope with the drought if you forget to water; would not die down in the winter, though might need protection in exposed areas, and you can use it for culinary purposes.

What about good old fashioned Nasturtiums? They will trail.

Good idea Arbuthnot! I have the Nasturtiums which were going elsewhere (but it's not made) and the chimney pot - so looks like that's it!

Thanks everyone, I was hoping to use a perennial, I will look at the suggestions thanks

Although not a perennial Dawn, trailing Verbena flowers all summer and often comes back the next year. How about strawberry plants?!

Thanks Sheila, I’ll have a google

Creeping phlox. I've got 8 in various pots, they tumble down the sides and look beautiful. They increase in size every year too. As a matter of interest, I've got two chimney pots but can only put flower pots in the tops of them as they have no bases.

Camomile, thank you, sounds exactly what I need. Yes, I've put plant pots in the tops of my pots too. Would the phlox be the stolonifera variety?

I don't know if they are stolonifera or subulata, I thought they were all the same. All of mine are trailing though, I've got six. I'll post some pictures, but they've nearly finished flowering now.

Thanks Cammomile, thinking about it, all phlox creep don’t they, I’m going to get some, looking forward to seeing your pictures