Your best bet is to buy the tubers or see if there's any specialist shops selling seeds in the colours you need...sometimes, Thompson and Morgan do some good individual colours.

Btw, where are you in East Sussex DrC ?

I've popped in here just to see others' answers as I'm also attempting to grow 'Bishop of Llandaff' from seed.

grow them in pots and plunge the pots into the border. if they start to show the wrong colour then just swap the pot. Specialist seed companies may well sell specific varieties.

grow zinnias instead......

Thanks everyone it looks like its tubers again next spring.

Oh Rats!

Zinnia would work SG?
Sorry about that Nariz and 'Bishop of Llandaff' is the only one colour seed I have been able to find for sale too and they are the wrong colour for me.

What colours are you looking for?
What shape, height and size do you want?

I want pinks to mauves and white, but not red or yellow to bronze, I like the shorter ones about 18" and I prefer shapes such as the Paeony and single flower ones but not the Cacti or Pom pom so much.

http://www.hallsofheddon.co.uk/home

http://www.eurodahlia.com/

are the two best suppliers with the most choices of what you want.

Both are very helpful if you give them a phonecall explaining your needs.

Well thanks for that, you are good as they look great sites. I look as if I will be spoilt for choice.