Yes: A solo swim you have complete a swim of at least six hours in a water temperature of 16c or less.
For a Relay you have to complete a swim of at least one and half hours in, out for a minimum one hour, one and a half hour maximum. Then return to swim for one hour. Water temperature of 16c or less.
That has to have been done during the 18 months* before your Channel attempt. *Please check the federation you are swimming with for updated details.