It's a tricky one this, plants are always easier to identify when in flower but when they are young it can be much harder, particularly with plants like this as comfrey can be edible and foxglove certainly is not!
This is comfrey
This is foxglove
See what I mean, they look quite similar don't they? But you really can't get these two mixed up, some people eat comfrey leaves (fried in batter) but they do contain an alkaloid that is toxic to the human liver, however you would need to consume quite a lot for it to have such an effect, foxglove on the other hand is quite poisonous, and a few handfuls of these leaves would find you in hospital very quickly indeed.
this is a comfrey leaf (underside) you can see it's shape and the fact that it is smooth around the edge, look closely at the stem too and you'll find that it's sparse hairs that are almost bristly
these are foxglove leaves and you can see just how hairy the leaf stems are, in fact they feel almost velvety, the leaves are also slightly serrated around the outside, (enlarge the top pictures to see this).
Good luck in your early spring foraging and be careful and sensible with what you pick.