I would wait awhile yet. Depending on where you are in the country, there is still risk of frosts for a few weeks yet. Keep them safe until all risk of frost is over?

Thanks for the advice, I'm in Cornwall, but I don't think we are frost free just yet. I will keep them tucked nice and warm in the grennhouse for a few more weeks.

If it is a heated greenhouse, be sure to harden off before planting out, though.