Traditionally St Patrick's day is when to plant 1st earlies, but I planted mine a week earlier.
This may seem strange because of our very late spring, but there are two things you should know:
1) The tubers are hardy and the foliage that is under ground is protected from frost. I plant my potatoes deep so that the foliage (after earthing-up) does not break surface until early May.
2) I planted them under cloches.
Mine are Maris Bard; not the most popular variety, but a flavour I love, and Epicure, known as "Ayrshires", the new potatoes I grew up with in Scotland. What variety are yours?