Tricky perennials from seed?

Sow them in small containers that can go in the fridge if need be.

Sow them according to the directions (some like light, so are not covered, some need dark so cover) and then leave them for a month to see what happens. If nothing happens then put the container into your fridge for a week or 2.........but keep an eye on them cos sometimes they start to grow in there
Then bring them out onto a warm windowledge , they should grow then.

The other option is to sow in Autumn and let the weather outside do the job for you 

Thanks.  I'll have a go at sowing them in modules then.  I am relieved to know that if that doesn't work, it will be autumn and I will still have time to try again outside  . By the way, I looked up London Pride and might just have to try those too!