Parsnips with curled up leaves

[mrshopeful]

A couple of my parsnips that were growing well now have leaves that are all curled up on themselves, I've tried unfurling them to see if there's anything in there but can't see anything.

Is it some sort of aphid or something else and should I worry about it? If it is a problem any help on how to fix them would be welcome.

Cheers