alright mate, what I tend to do most years is wait until the LAST FROST is over, last year it was about mid april I think, pretty late.

I usually germinate mine by putting them into distilled water and leaving them for a day to sink, then put them into clean soil with no nutes and put them under lights for about 2 days, after they have risen just put them in a greenhouse for another 2-3 weeks then they should be big enough and strong enough to survive outside in the UK