Either in early spring under glass at 13 - 18 degrees, or in situ when all danger of frost has passed.

Hi Lollipop! I live in Somerset, too! Welcome to GOY. I hope you enjoy it. :-))

yes I agree, early spring with bottom heat. I have a vague memory that you soak them in hand hot water for about 10 mins to help break seed dormancy. but you had better double check on that. [memory suggests they are called the hot water plant too.]
welcome to GoY too.

Isn't that Achimenes, Sbg?

yes you are right. knew there was something wrong with my answer. bless you spritz.

Aaaaattchoooo!! LOL.